in terms of the raptor - get it! even though it advertises a slightly lower read, write, access time, when it comes down to it, the hdd is what u wait for. Also, take the access time and multiply it by 3 and thats the REAL access time with a few huge files on it and such. What may seem like a fraction of a second is an eternaty in a computer... I don't know how you can have a hard drive full that is 150gb's... i have the complete simpsons and family guy seasons (358 simpsons and i think 50-ish tracey ullman shorts; 70 family guy) as well as nearly 6000 mpeg layer-3 audio files (mp3), with 13gb's of programs (in the program files folder) and 10gb's of files such as itunes setup, 3dmark06 setup, etc. this isn't even including all of my misc files such as the drivers, my programming files (partially built operating system im making, c++ files, php, python, 100 web pages, and so on..).
Anyways... go for the 2 7800's for better performance, but the 7900 will be cheaper. and i would TOTALLY recommend the raptor