From what I've seen they're not too far off on CPU, the higher end variant is about 8-9% faster on multicore.
They differ a lot more on GPU, and I've seen a bit more variance in their Metal Scores, but it seem like the higher end chip is anywhere from 24-28% faster for Metal.
The cooling system seems good enough on the 14", which has High Performance Mode for the first time in a 14" MBP. I was just watching this video:
where they compare two M3 Max 14" and 16" and they are pretty close on most tests within a few percent, with the 14" slipping behind a little when under sustained load, and it seems more evident in Premiere Pro for some reason. But the 14" M3 Max still beats out the M2 Ultra in that real-world test! So that's pretty significant. And gaming it seems like a more middle ground difference of about 8%. We're talking about computers that are so fast here, that the form factor you want is honestly probably more important than the speed. Get what suits your needs best for size.
Edit: It's also important to note that the 16" in this test has twice as much RAM, so that might affect video apps more in particular.