Honestly I wouldn't consider the 7990 until the frame pacing driver comes out, which should be late July or early August. There are stuttering issues that need to be addressed with that driver.
Out of the other cards you mentioned the Lightning should be the best overclocker. If you don't plan to overclock very much, then the cheapest of them should be at least able to match the lightnings stock settings.
If you have no plans at all to overclock the lightning/power edition will have better stock performance then the others, but at a higher price.
I personally would buy the cheapest of the cards and overclock to match the lightning manually. That way you get the best bang for buck. The 7900 series are known to be really good overclockers, and most i've seen reviewed hit 1100-1200mhz core clock quite easily if you up the voltage a tad bit.