your ok using high wattage
psu's with low requirement hardware, they just won't draw as much.
Basically apart from SLI or dual processor systems you only need 350W as long as it's a good brand of
psu, I run a newcastle core, 1gb ram, 2 hdd's, 2 optical drives and a 6800 off a 380W
psu without any problems.
The
psu I've recomended will definately suffice for your system, your looking at an average power usage of around 200W full load and 100 in normal use