Next to Upgrade?

[Anaximander]

ye SLI / Crossfire isn't all what it's cracked up to be. Not all games support it fully, and you never get access to the full juice of both cards combined. Also micro-stutter and insane power consumption / heat development theoretically stressing other components in the PC.

In general, unless you find an extremely good offer on a SLI card that matches the one you have perfectly, just go for 1 good card, something like the Radeon 79xx series or Geforce 7xx series. Tom's Hardware are always updated on where to get the best "bang for the buck".

If not that, I'd look at an SSD, a 23" Full HD screen (they're cheap at the moment) (scratch that, I just noticed you've got a 3 screen setup) or a PCI-E 3.0 mobo / intel i-series processor as future upgrades (and get a wired internet connection ).

EDIT: Also I think Star Citizen, if everything they keep saying is going to hold true, is going to require another upgrade anyway when it's out. It's going to be super taxing on any current system.