I did a similar upgrade on my C280. I upgraded the fronts to SRT diska and calipers. It all works well, but the long initial brake pedal travel is unnerving. I have investigated upgrading the master cylinder, but Centric seems to think they use different pushrod heights, and are thus incompatable. I have spent time to determine if this is true, but without success. I do know when I upgraded the brakes on my 190E to 500E brakes, I upgraded the master cylinder to the 500E at the same time. I did not have any pedal feel issues at that time. In the reading I have done, it is indicated when you increase the piston size in the front brakes you do need to increase the size of the M/C to maintain the brake feel. Let me see if I can determine if the C280 booster and the C43 booster are the same. If they are, I can upgrade the M/C. If I do, and see an improvement, I'll post the results here.