How much impressions is good for testing? lets say If my ad is running 4k imps with a ctr 0.02 should I ditch it and move on with other well performing ads? or the impressions is too low to tell and I should wait a while see if the CTR increase or not? Currently my highest CTR ad is 0.057% with 3.5k imp don't know if I should tweak it or just start making some new ads until I find the sweet spot. Any suggestions?