If you think it vibrates a lot at 3000 OPM's, then you have sensitive hands! The only time the counter=weight is going to come into play is when you use the machine at 6800 OPM's and with a heavy back plate. With the combination that you are running at those speeds, the counter-weight is a total none issue. You are not working the polisher fast enough to be concerned. The vibration you feel is normal.
Don't over-think this, just continue with your paint correction. Also, never work below 5000 OPM's when removing scratches unless you are using a thick, paste type swirl removing compound and are doing the slow cut process with the PC. Other than that, stay at 5000 OPM's (if you are using my technique), with 9-14 pounds of pressure including the weight of the polisher. Only when applying wax will you drop down to 3000 OPM's.