Most of the SLI issues with Windows 10 have been worked out but from my personal experience, although many will argue with me, Windows 10 has been nothing but headaches. I have rescued and rolled back all of my PC and a laptop from the brink of disaster except for one. I don't use that PC much and it isn't SLI capable but I have absolutely a ton of Errors and Warnings in my Event Viewer every time I turn it on. I get OCD about those things. If you want your free Windows 10 license I believe you can upgrade and then roll back and then your Windows 10 license will remain valid for later use since it is registered with your hardware at the time of activation.

Running a GTX 690 in SLI with no issues on Driver 362.00.