I never recommend SLI unless you have a great budget, like going for two GTX 980's for example. Other than that, performance with SLI/Crossfire cards are usually very inconsistent as they don't perform well in most modern games as they are optimised for console instead. Look at games like AC: Unity, Far Cry 4 and Battlefield 4. They are not good with SLI at all. It's possible in BF4 but very inconsistent too.
For the price you can improve your processor, take that in mind first. I'd say you have the money for an i5-4690k, don't miss out on that. It's really important to have such a quality processor and I wouldn't miss out. Looking at your budget, something like this would be more ideal:
PCPartPicker part list /
Price...