One other thing, from all my research, overclocking GPU doesn’t offer much performance gain for our use. Overclocked CPU, different story. If you overclock the CPU or GPU make sure you have sufficient cooling or it will be unstable.
Take a look at Xoticpc.com , I’ve had tremendous success with their machines. I’m on my forth machine from them and all have been overclocked machines that were rock solid stable. I could count the BSOD’s over the years on these computers on both hands and have plenty of fingers left over.