Wait for windows 10; stick with what you got. Win 10 is doing free upgrades for everyone with win 7/8. Just keep using your key bro.
And from everything I've heard/seen of win10 it's actually going to be a good release. I have yet to hear anything really bad about it at this point.
Also, from what I hear, win 8.1 runs bf4 better than 7 because of directX optimizations, better multi-threaded application support, amongst other things.