You'd need a new motherboard to move to Skylake or Kaby Lake, and the performance difference between Haswell and Skylake/Kaby Lake isn't very big, only around 10% clock for clock. If you feel the ned for a new CPU, your best option would be to get an i7 4790k. Supersampling would involve the use of DSR to run resolutions higher than 1080p or bumping up the resolution scaling in game. It is sounding like a CPU bottleneck, the large player count servers drastically increase CPU usage, and that might be why you're getting better performance in game modes with smaller maps and fewer players.