From your description, it sounds like you may have some broken teeth on your front sprocket. Odd at 6500 miles. Maybe a pic would help? If you are going to replace everything, I would suggest that you go up two or three teeth on the rear sprocket, and stay at 15T on the front. The 15/43 combo is VERY nice and is what I am currently running. At 80 MPH in 6th gear, my engine is turning around 5000RPM. Very good pull in the first few gears. 2nd gear throttle wheelies are possible (not that I would recommend that ). If you do not plan to replace the rear sprocket, you can go down one tooth on the front (which has the same effect as going up 3 on the rear). There is probably some disadvantage to doing this, but if there is, it is very negligible. Ducati 748/749s come with a 14T front from the factory. I ran a 14/40 combo for over 14K miles with out problems.