I would get a better graphics card. Crossfiring two 7770's probably would get you close to the performance of a 7950 but would not exceed it. The 7950 woud give you more bang for the buck. Check out this comparison between the Radeon HD 7770 vs. the Radeon HD 7950. Keep in mind that adding the second card does not quite double the performance, it's more like 80-90% improvement.
well there is a 3rd way!!
u could get a 7870 and a 60GB ssd.
dont get me wrong, 7950 is an awesome card, but if u play in a single monitor in 1080p a 7870 is still more than enough for ultra,
and the ssd 60GB is not for games, since it doesn't increase gaming performance in games anyways. just improves load times.
the 60GB is enough for OS and all the other software.
that's wat i would do.
remember any cheapass ssd is still a huge step over the hdd
The third option has its merits: The HD7850 is a potent card, equal to my dear departed 6950 and that was plenty for all but the most demanding titles: Yes, Im looking at YOU, Metro 2033! (still looked great @ DX10, High, 16xAF, AAA, though).
If you're the type who wants to play Metro 2033 at Very High, DX11 though the 7950 is the way to go (love mine btw).
One last point: What is your monitor resolution? If you're playing below 1080 res then I'd say option three is the best solution, in this case you could have your cake and eat it too.