Between the time you got 200Fps to the time it dropped to 50Fps, did you update drivers or install antivirus software, etc. This can have an effect on the performance of your GPU but highly unlikely. You might even want to try reinstalling your drivers. Use Driver Sweeper to clean your old drivers completely and reinstall, then I would also recommend that you download MSI afterburner, activate the GPU settings on the On screen display and monitor how much GPU% the game uses. After installing a fresh version of catalyst, do not fiddle with the settings, leave them as is, then see what the performance is.