if you want the ultimate multi moniter set up, the 6970 + 6990, if you only have 1 monitor then that will pretty much be able to max everything out for a while
CF 6970 will be more than enough for single monitor use, but the 6990+6970 will make it more future proof.
Personally, im saving up for a 6990 right now, so if you have the budget, by all means, the 6990 should satisfy your graphical power needs for a lonng time
the 6990 is basically 2 6970 running a slightly lower clock, and the entire set up runs as fast as the slowest card, but the 6990's overclock pretty well so thats not a problem, especially if you water cool.
onyl one con though, the 6990's get a bit loud
if anything, if you run a intensive game, your cpu would probably bottleneck first before even reaching the potential of the 6970+6990 setup
Edited by mnkeyprince - 10/28/11 at 4:19pm