I think the pistons in your calipers may be binding a bit. The front pads on my SDL have almost 30k miles on them, and are near dead, I'm waiting for the light. But the braking has not changed, I was doing some heavy braking today and the pedal effort the same even when the brakes were real hot.

Perfromance seems to have not changed either.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200