Computers are not as logical as they sound...
Graphics cards:
More RAM doesn't make them faster.
Clock & Memory MHz doesn't directly relate to performance.
Brand has nothing to do with performance - if you buy a cheap, slow card it will be cheap and slow.
PSUs:
The colour or the wattage don't make a PSU good or suitable. A grey 430W PSU of mine outperformed a blue anodised 550W PSU.
Some things you can go by are the price, brand, whether they have PFC (active preferrably) and also that the efficiency is at least 80%. Good brands in my experience are Seasonic, Hiper, Coolermaster, Jeantech, Antec, Corsair. I normally go with Antec as they are reliable and not overpriced. If you like loud bangs and rebuilding PCs then you should spend less than ?40 on a PSU.
<tangent>CPU speeds are not related to how many GHz they have</tangent>
As for graphics card suggestions, my spare PC has had an ATi 4670 and a geforce 9800GT, ?55 and ?80 respectively (a year or two ago). Both did a fine job at Oblivion and LAN games such as HL2DM, GTA:IV, L4D and BF2, although only at 1280x1024. GTA:IV wasn't maxed out, but for ?55 I was impressed. At 1920x1080 you will need a faster card, but you get more for ?100 now than 2 years ago.
For choosing graphics cards I always go to
http://www.tomshardware.com and check out the graphics charts to see how the different cards perform, and then pick some cards I like the performance of and check their prices, see which ones work out cheapest for the performance.
Can't proofread what I wrote or expand on anything, gotta go now!