What I was thinking, now to find out if it's less expensive buying two 5870's or one 5970.
I did the math before I brought my new GFX card, the 5850. By looking at various online charts, 5870 costs an extra £10 per FPS over the 5850, I wasn't willing to pay an extra £100 for the 10 extra FPS the 5870 offers, when, for an extra £100 I could get an additional 5850 with a massive boost in performance. I could even buy 3 5850's for the price of two 5870's at the time.
5970 > 5850x2 > 5870x2 if you were to compair price/performance.