Soldato
1080p.
Well it's no wonder you're getting less than idle SLI scaling. That resolution can be handled by one 680 (most games) so the extra 680 is going to result in underutilization perhaps even negative scaling in some games.
For new games without a mature SLI profile or if you don't know how to set it up using nVidia inspector then you'd perhaps get better performance using just one card.