i have owned both the 243 and 6mm which i currently do own. I have to give teh edge to the 6mm that extra 100-200fps diff makes a lil bit of a difference on long range shots. As far as actual on game damage and preformance i cant really see a difference. My 6mm is by far more accurate than my 243. the 243 with handloads would shoot inch groups my 6mm off the bench with my handloads will cut holes at 100yds as long as i do my part. I'm fairly partial of my 6mm i dont think im gona put it down here anytime soon, though i would not hesitate buying a 243 sometime. To each his own.