I heard that Minecraft doesn't take advantage of SLI (which sucks) . Also, you're in a flat land area which if you went to a forested or mountainous area you'd get even less FPS. Or not depending on your system.
I get the same no matter what, unless I record then it drops to 10-15 due to well movement, recording stuff and well chunk loading... and yeah not many games take advantage of SLI, but the ones that don't often don't drop in performance like minecraft does.