yeah i think you better to go with the GX2 (when prices drop), more futere headroom (you can SLI later), its a better performer anyway, but youll need a better PSU...
If you have two ultras already, then hold on to them for just abit longer. The new cards are not that much of an improvement over the previous generation's high end cards. Wait for a new core to come out before you upgrade, most of the new ones seem to be based on the G92 chip.