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The system I started with:

Mid 2011 iMac 27"

| Memory    | 8GB 1333MHz DDR3                 |
| HDD       | 2.7GHz 1TB (7200 rpm)            |
| Graphics  | 2.7GHz AMD Radeon HD 6770M 512MB |
| Processor | Intel Core i5 2.7GHz             |

The system I currently have (only changes listed):

| Memory | 32GB 1333MHz DDR3                              |
| HDD    | 4.0TB (5900 rpm) SSHD Solid State Hybrid Drive |

(Memory is OWC Memory Upgrade)
(HDD is From Seagate)

The System I want

| SSD       | 120GB 6G SSD Optical Bay Hard Drive Replacement     |
| Graphics  | Mid 2011 iMac 27" Radeon HD 6970M 2Gb Graphics Card |
| Processor | ...?                                                |

(SSD is OWC 120GB SSD)

I'm not as impressed with the HDD as I thought I would be. It is way better, but it is also way more than I need. I have just under 40GB of consumed storage on my system (i.e. currently 3.96TB available), so with the 120GB I can make a 60GB partition for the entire system (startup, apps, files), and another 60GB partition for another drive (storage, OS, whatever). The 4TB HDD will be for deep storage, should I ever need it.

I am confident the GPU upgrade will work. Apple also has technical specs stating that the graphics are "Configurable to AMD Radeon HD 6970M with 2GB GDDR5".

Stuck!

The processor is where I'm having trouble. Hardware is not my schtick, and there are endless feeds talking about various processors, and whether or not they work.

One person might say that "You can only use an i7 core Apple offers as a OEM upgrade or you'll have firmware problems."

Another person might say that "they're using a "regluar i7-2600" and having no problems.

And finally, another peron might say that the "Core i7-2700k (3.5ghz)" will work fine in the 2011 iMac.

But which is it!? Will any old processor do?

My Research

About all I know with processors is they need to have the same socket (for this iMac, it is LGA 1155), and compatible RAM ((for this iMac, it is 1333MHz DDR3).

From there, I've narrowed it down to five Intel Core i7 Processors (all five compared on same page after links):

  1. Intel® Core™ i7-2600 Processor (8M Cache, up to 3.80 GHz)

  2. Intel® Core™ i7-2600K Processor (8M Cache, up to 3.80 GHz)

  3. Intel® Core™ i7-2700K Processor (8M Cache, up to 3.90 GHz)

  4. Intel® Core™ i7-3770 Processor (8M Cache, up to 3.90 GHz)

  5. Intel® Core™ i7-3770K Processor (8M Cache, up to 3.90 GHz)

... Here is a one-page comparison of all five ...

But from here, I really don't know what any of it means. Bigger numbers often mean better (more cores, higher processor frequency, more memory, faster speeds, etc), but this isn't always the case.

They are all within 0.2GHz, which is hardly noticeable or worth splitting hairs over. Same number of cores. Same cache. Same max memory. Same package (ignoring FCLGA1155 from LGA1155). And the rest is basically identical between them, with the occasional differences that I likely don't understand.

One standout difference for the 3770 series are that they both have lower Thermal Design Power, which will help with internal cooling and fan noise. BUT, the same series is also the only one without Intel Fast Memory Access, which sounds pretty great!

On top of not being able to adequately differentiate them, I wouldn't know if any of these processors is/is not compatible with the graphics card and other components I've set up, or if they'll sun with my current OS.

Just to recap, the hardware:

| Memory   | 32GB 1333MHz DDR3                   |
| HDD      | 4.0TB SSHD Solid State Hybrid Drive |
| Graphics | Radeon HD 6970M 2Gb Graphics Card   |
| SSD      | 120GB 6G SSD                        |
|          |                                     |
| OS       | macOS Sierra (10.12.1)              |

I've read multiple successes for getting non-Apple processors to work by deleting AppleHWSensor.kext. Maybe this won't even be required.

Can You Help Me?

  1. Can any one of these processors be used for my upgrade? Thus making the real deciding factor the features, cost and availability?

  2. Or are only some of them suitable candidates? Which ones? Why?

  3. If the first is true (any will work), is any particular processor more renowned than the others? I'm trying to stay away from opinions for this question, but maybe one or two of them are known to be industry go-to.

The End

  • This question is a good candidate for the SE Hardware Recommendation site. – fsb Oct 26 '16 at 0:06
  • @fsb thanks for the suggestion. I put it up there, mentioning that it was on here first. There are so few tags though, and since I just joined it, I cannot create any myself. We'll see how it goes. – Birrel Oct 26 '16 at 1:36
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1. How to choose a compatible CPU?

The basic rule is to use what Apple uses in different iMac models:

As shown above, these are the five CPUs that iMac 2011 uses in different models.

According to your question, your current CPU is Core i5-2500S@2.7Ghz. So, in order to prevent possible compatibility problems, we have three options: (In Socket1155 CPU)

  1. i5-2400@3.1Ghz

  2. i7-2600S@2.8Ghz

  3. i7-2600@3.4Ghz

Perfomance: i7-2600 > i7-2600S > i5-2400. So is the price, and they are all more powerful than your current i5-2400S.

Suggestion: Now as you want an upgrade, i7-2600S is the best choice in both relatively lower price and enhanced performance.

2. Why not use CPU with "K"?

First: K represents "unlocked" and "Overclock", which enhances the performance of CPU and requires motherboard support as well. I think you don't have the need to overclock CPU.

Second: find some questions on changing CPUs with K processors, some of these questions report system problems.

3. How to really boost your system?

Changing the CPU might matter. But as I have been using both i7-2600 and i7-3770, I cannot tell their difference when using iMac except that you have tasks bringing heavy load on CPU.

Changing to the SSD is what can really boost your system. Actually, poor speed of regular HDD is the cause of poor system performance.

  • I agree with @bret7600, your answer was very helpful. In my particular case though, a better CPU is important. Check out my other post, regarding my system not utilizing memory. The important bit (on why I need a better CPU) is in Edit #1. I'm not trying to direct you over there to answer that question, but rather the whole question explains why I need to upgrade. – Birrel Oct 26 '16 at 6:27

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