The old i5-2500 could drive a trio of GPUs so it's not the CPU. Most folk move away from SLI today since a single card is less trouble and current cards could best the dual 660.
I think the PSU should be fine since a dual 660 load should be more than a 1060.
As to best 1060, I think you are picking out that on your own since differences are usually slim. You can find what you can buy today and find benchmarks to pick your winner. No one I know will find all dozen or more 1060 to find the best since it's a waste of time since the winner may be out of production or sold out. You have to supply your short list to expect members to do that work. Try 2 or 3 cards at most.
Hello my current problem is that im not sure what graphics card i should upgrade too without bottlenecking or any sort of problems. My current setup is
Mobo-Rampage IV Formula
CPU-I7 3820
GPU-GTX 660 SLI (2 of them)
RAM-16gb (ddr3)
I want to upgrade to the best video card possible for this cpu and mobo!! Minimum 4gb vram!
Thank you so much in advance
Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic