Seems to me some confusion on this thread. The user doesn't seem to be saying that he is getting poor perofmrancep er se, only that it's actually getting worse when using dual GPU's thus this is not going to have anything to do with a CPU bottleneck.
The issue is going to lie generally speaking as driver level. SLI/Crossfire at best a finicky things to begin with and when you start mixing in newer hardware with newer drivers into an older game is where you are going to start seeing issues. You could try older drivers and see what happens but to be honest I think this is going to cause you more incompatibility issues overall with your PC than what it MIGHT solve with SLI in this game.
Generally from observation the people who have had greatest success with SLI were people on much older GPU's - the general complaints for SLI and this game come from newer GPU's which leads me to my above conclusions.
As to why you only see 50% GPU utilisation ( seperate issue from SLI ) then that is generally due to indeed most of the instructions being needed to be completed by the CPU as opposed to the GPU ( simplifying things here ) thus in that regard in does indeed become the bottleneck. Interestingly though with the new AA options I've at least managed to get the game to max out my GPU ( r9 290 ) though I'm wondering if this is more a driver issue than what "should" be happening becuase it occurs even on medium AA and I get really bad performance. NOt really playing the game play itself ( just doing GTN stuff, crew skills daily ) until 4.0 so haven't bothered trying to fix yet.
The key to it all is really what sort of performance you are getting on 1 card and is it in relation to the CPU you are running? I.e. you should be getting 100 FPs in most zones with drops to 50+ in WZs/OPs I would think at that CPU speed.
As for SLI if you've tried most suggestions then not much else you can do beyond playing with different drivers to be honest.
