True. Wait, False. Wait, what's the question? :P
Two 6970's should outperform both your current setup and a 7970 by a substantial margin (the wild card is how large of an OC you can hold down on a 7970). 6970's are fairly inexpensive right now- can be had for as low as $300 a piece after MIR. Note: 6950 unlock to 6970 is not very reliable these days and as I understand it many cards can't do it.
The other option is a pair of 6950's or 560 ti's which can be had for sub $400 after MIR if you find a good deal.