You cannot get too much PSU for your hardware. However you can get too little. It is never a good idea to stress your PSU to 100% capacity (or anywhere near there) and as a rule of thumb, I try to use 66% capacity peak. Not only will your PSU last longer, but it will operate more efficiently, and cooler. I got the Thermaltake Toughpower 750w after Christmas for $99

I use the CNPS9700 on my Q6600, they work great.