Yep, mobile i5 has a passmark score of 2718 whilst the desktop version is 6809.
If you're looking for outright performance, always go for the desktop model. In saying that though, try to go for the i7 desktop model if you can; you'll get much better performance because the i7 is hyper-threaded for 4 virtual & 4 logical cores, whilst the i5 just has 4 logical cores.
My 15" MacBook Pro outperformed a 2011 i5 iMac which had 32GB of RAM in Logic 9. When opening the same project on both, the iMac's CPU just gave up and was at 100%, giving a crash error. As the 15" MBP i7 is quad-core & hyper-threaded, it handled this without any problems.
TL;DR: for performance, go for the iMacs compared to the MacBook Air. Don't underestimate how powerful the 15" MBP is -- for the same price point you often get better performance than an iMac for the same value (unless you go i7 on the iMac).
And in future you can go to
www.cpubenchmark.net to check benchmarks on certain processors.
