Well 7850 crossfire will perform better than a 660ti. The 660ti is about 30% to 35% stronger. So 7850 cfx looks like it will perform a little better than a 680. So a 7850 will be better but a 66ti leaves more room for upgrade in the future. Yes crossfire is more difficult but it will work better. if you sell your 7850 you could probably get it for about 100.