I'll rephrase, no real humanly observable difference.
Youch! Looked at the benchmarks for that A10-5800k CPU. Scored less than half my i7-3770k! Ok so maybe some observable difference.
But I still think a new gpu will give him the bigger boost in gaming performance.
Just for comparative purposes, his CPU was listed with a score of 4637 vs a 3770k of 9589. Big difference but I believe his will still handle games. When you look at the score of his 7660D gpu, i think it's clear where his biggest drawback is at the moment.
7660D - 796
GTX660 - 4121
Depending on costs, I'd might consider getting a new motherboard with an i5 and an 8-series nvidia card. Lasted graphics cards are always overpriced in my opinion.
"I like offending people, because I think people who get offended should be offended." - Linus Torvalds