Depends on the features you enable in FSX as to whether GPU plays a major role or not (it's still heavily CPU dependant).
But here's the thing, unlike what was initially said by OC, the wait is short, and worth it for 2 big reasons;
A) it's a new series, with new features that may or may not have improvements at doing certain things in old and new games. DX11 or not, they may handle certain functions and dependant ops better and may handle threads or memory better, and this would help or might eventually help (with a patch) some geo heavy titles.... ...like some simulator games. Regardless of DX10, the G80s dominated many shader and texture heavy games because they were simply more efficient at things that held games like Oblivion back and finally let people crank them to 11 with things like the QARL texture add-ons.
This may or may not be the case this time around, but really it's about to be revealed in a few weeks, not a few months, isn't it worth the wait to find out what's new and what it means?
B) ANY new launch puts downward pressure on cards, either just before or just after launch, and for this alone, if the HD4K or GF GT# is not something you absolutely need right now, then waiting is unlikely to cost you money.
Once again, since it's a few short weeks (almost feels like a few short days) until launch, and not a few months as previously postulated, then it's worth waiting in these rare cases.
IMO, my general rule is that it's worth waiting a month or so, but not many months for hardware, unless you already have something good (like a GTX280) and there are no/few 'value upgrade' options anyways, then it's simply a question of being worthwhile holding off and not wasting your money period.
Waiting sucks, but so does jumping the gun right before a launch.