Not worth the upgrade unless you do massive rendering/encoding. For games your CPU will do just fine, what you need is a better GPU. The frame loss you get for not having L3 is minimal, maybe a 2% hit at the most.
Forget about stock voltage if you want to get the most out of your CPU. With a decent CPU cooler you can get your 620 to around 3.4/3.5Ghz easy while attaining low temps.
Invest in a 5770 or 5830 if you want more performance in games. Your CPU is more than fine =)
yup going to keep my cpu i was looking at a phenom 965 BE 3.4ghz stock overclock it to 3.8ghz
but I'll just get a 5770 most likely