e8400 has no problems overclocking.
http://valid.canardpc.com/kz8mzl
g41 chipset usually tops out on fsb below 400.
So @ 343..you're about at that chipset's limit.
see if there's jumpers..
If you want to overclock with 775,you need a p35,p45,x38, or x48 chipset.
G41 will do it a little..but not much.