I just remembered another bug with the physics that keeps slowing me down, and it's when a ramp is around 45 degrees (or only 45 degrees, can't say for sure), there's a chance for you to get stuck on it. I think I remember this being an issue in Q2 as well unless you use a high enough fps, like 120 for example. Don't know where the limit is though.
It's very apparent on ice jump maps where you speed up into a ramp, but it's also a frequent problem on normal maps as well.