Is Snow Leopard or Lion faster?
And how significant is the speed difference?
There's very little difference.
Check out this cnet review it shows the performance of applications like Photoshop, Call of Duty 4 etc. on a 27" 2011 iMac running Snow Leopard & Lion: http://news.cnet.com/8301-17938_105-20081987-1/snow-leopard-vs-lion-performance-head-to-head/, which concludes: