I've got the Early-2015 13" MacBook Pro (2.7 GHz i5) and whilst I was building Smart Previews for all my 1600+ photos in Lightroom 5 I noticed that the fan had come on (unusually) and that the laptop was starting to get rather hot.
When I had a look at Activity Monitor, I saw that Lightroom was using around 300% CPU. Fair enough, I'm sure it's an intensive process. However, I also saw the usage for Lightroom jump higher than 400% on several occasions (usually up to around 410%).
I understand how my CPU is Hyper-Threaded so that it has 4 cores/400% CPU available, but how could it possibly use more than that (bearing in mind several other processes were running as well)?