In a mid end gaming computer which would be faster this or this. I give u teh specs:
AMD Athlon 4000+ (makes my comp start slow and crash a lot)
NVIDIA 8600GT
2GB Supertalent OC @ 890MHz
320GB seagate 7200RPM HD sata
MSI K9N Neo-F v3 (socket AM2)
I don't know a lot of stuff about cooling and heatsinks etc.
But for the PSU, there's some calculators where you put in your hardware and it gives you an estimate of what PSU you should get. Remember though, it's an estimate, so to be safe I would get one a tad higher than the calculator says.