No point in spending twice as much on memory when that money would be better spent on a better VGA card for a gaming PC.
I'll be surprised if PC games start requiring more than 4GB of system memory to run properly any year soon.
And buy a quality PSU. While PSU failures don't happen happen on a regular basis, there's no point in risking a decent system with a generic PSU, especially if you plan on doing any overvolting/overclocking.