but those SLI AM3 mobos are not that future proof since they don't have SATA3 an USB3. On the other hand you have plenty of crossfire good AM3 mobos if you don't have already the video cards. You can go for two HD 6850, for great performance.
Also if that's for gaming (you want dual GPU) the Phenom II X4 are cheaper and even better in gaming.
That's good for Nvidia, the HD 6850 takes only 127 watts on full load each (a factory overclocked 460 about 200W) but more power never hurt anyone.
The factory OCed 460 are faster thanm the regular 6850s but you can OC your 6850s to the HD 6870 level or buy factory overclocked ones as well (XFX HD 6850 Black Edition, Sapphire HD 6850 Toxic).