The way I try to decide what power supply I need, is I figure out how much power the GPU needs, and then I add 250 watts or so. It’s not a perfect system or anything, but it hasn’t failed me yet.
If your computer can support it, I suggest nabbing a Quad-Core or an i7. I upgraded from a dual core to a quad core (my motherboard is not compatible with i7’s) and my performance is more than doubled in every game. It’s amazing!
That means your CPU was the bottleneck in your system, the CPU is not the only thing that’s important in a PC, especially for gaming.
Your advice can be misleading, for example for people with built-in intel graphics, they can upgrade to the fastest quad core on the market and still get 12fps in Half-Life 2…