I've got a 7450 too.
Rock solid at 800 mhz with VCore 1.59.
If you get a lot of lockups, causes to look for before changing VCore:
1. Memory
I had loads of lockup-problems with Linux, disappeared with a change of memory.
2. Cooling
Try running at 600 mhz a while, if you get a more stable system, then it seems to be a cooling problem
