I have been trying to decide if there will be a substantial difference between the i5 and i7 processor for compiling and running VMs. I expect to run Windows with Visual Studio in a VM as well as a lot of XCode. I don't know how much difference the following benchmark and processor differences will translate to in compiler performance, especially if running them in a VM.
I looked at the Geekbench3 and pulled out the following figures from the averaged charts at Primate labs comparing the two Macbooks against my current desktop.
Benchmark 13” i5 2.8 GHz 13” i7 3.0 GHz iMac 2.5Ghz i5 21” Mid-2011 64 bit multi-core 6880 7209 10073 64 bit single-core 3294 3466 2663 32 bit multi-core 6151 6373 7103 32 bit single-core 3131 2971 2466
XCode can compile using multiple cores as can Visual Studio (at least if I boot with Bootcamp, not sure if will work under a VM).
Note that a common mistake is for people to think the i7 in the 13" Macbooks is a 4 core - it's not - both the i5 and i7 in 13" Macbooks are dual-core. The difference is the i7 adds hyperthreading. (The 15" i7 model is quad core.)
The other difference that may be very significant is the 3MB vs 4MB cache.