Yeah if you cant afford both just get a dual core than get a better GPU as there is no point having a quad core but a poor gpu as over all game performance would be bottlenecked by the graphics
As for what gpu to get well any 8800 card would be fine .If you cant a afford a 640MB model just get a 320MB as it will still be a very capable card
If he isnt planning to overclock you could take that cooler away and use the stock and then put the money from the cooler to a GPU
As for the raptors they are expensive per gigabyte compared to other hard drives but they perform much better in benchmarks i dunno about real life situations and so i would say if they are within your budget range definatly get one