Guys I think that you over estimate the power requirements and underestimate the quality of PSUs in today's PCs (whose efficiency is MUCH higher than before). My advice to Sa80 (who is on a budget) is replace your components and then see how it goes with your current PSU. If indeed you experience stability issues while under load, then go ahead and drop an extra £50 but I really think that its a discretionary purpose. I've been building PCs for 15 years now and I've never encountered a situation where instability was caused by a bad PSU. The big bad PSUs that have appeared these last few years are aimed at the so called "enthusiast" or "gamer" market, mainly young males with more money that sense. Bright colours, chrome, big stickers, etc. Makes me sound like an old fart now doesn't it

If you're serious about PSU check-out
this website.