If you can hold out nvidia is releasing new cards in May. This will flood the market with 980ti's, which should be your top choice. It all depends on what you can afford to. Windows 10 is awesome and I have been using it for all most a year will no problems. Remember when buying a video card, base it off of the monitor. If you use a 1080p at 60htz you only need a card that will hold 60 Fps on games. I highly recommend if you do pick up a used gaming one with a refresh rate at 144htz. Your game play will greatly improve. If you have anymore questions just ask, I'm here to help.
I use windows 10 with no issues whatever....
I had to roll my pc back (system restore) once as it wasnt running properly but I am not blaming windows update for it although I could never rule anything out......
hope all goes well!
BACK UP EVERYTHING FIRST!!!!
On an external HD, or one of those cloud services. Just in case... not speaking from experience or anything........
The only bad experience I get from Win10 is delay in videos playing on websites, plus Firefox and 10 don't seem to like each other.
Using Windows 10 and it works perfectly and much faster and better than 7. With graphics card of course make sure it fits in your box.....