6970 is better choice imo:
you have more VRAM
what're your full specs? resolution? 460 SLI is pointless, it performs very close to 6970, but has a lot of issues, they break very easily and consume damn a lot more power...
You forgot that they are mobile cards.
460M is full GF106 (GTS450) @ 675Mhz, while 6970M is 960SP Barts (HD6950) @ 680Mhz.