i7-8650U is rated at 2.1Ghz @ 25W in it's TDP up config, so running it at 20W may get you 2.0Ghz instead of 1.9Ghz. But this doesn't tell the entire story either. Modern processors are constantly adjusting their frequencies across all cores to hit their power targets. e.g. if the thermal management can't sustain 20W in perpetuity in may actually run slower than it's rated speed. Unfortunately this isn't something that is easy to determine from most benchmarking tools. Things like geekbench will only tell you the system could maintain certain performance for the length of the test, which is usually only a couple minutes, you may find that doing longer running work will cause throttling.

If you really want to know how it'll perform under heavy workloads, you probably want to hit it with prime95 or blender for 30+ minutes and monitor core frequencies to see where it ends up running at.

Do they really? Wow...fuck Apple. I have been using Mac for years but I don't want to pay that much for severely handicapped hardware. Especially when it's just in pursuit of thinness and aesthetics.

I assume that MikusR was talking about the i7-8650U. Apple doesn't down-TDP the processors in the MBP. I don't know where this idea even came from and it's trivial to prove it false.

This doesn't appear to be true. I tested my i7-6920HQ MBP with Intel Power Gadget and it reports 45-46 watts under load when on AC power, and 40 watts on battery. Reported speed is 3.1 GHz (official specs are 2.9).