1. Does it only lag when you are recording?
2. When in game, if you bring up the task manager how much RAM is being used? Are you running low?
When recording, my game doesn't lag at all just the recording comes out as crap, and as for the RAM recording with shadowplay only uses 6.75GB of my 8GBs of RAM When recording with OBS on the Other hand it uses 7.2 GB