I run an A4000T, Cyberstorm MKIII 060 66Mhz, CybervisionPPC 8Mb Gfx Card and 128Mb FastRam.
I get the following results on Amiduke:
320x200 8bit CyberGfx Screenmode - 21fps
640x480 8bit CyberGfx Screenmode - 11fps
Saying this, I do get a bit more in certain areas of the game, such as the falling down the pipe in the LA Meltdown scene. I get 44fps.. but thats not all the time. The above results are what I get with the normal gameplay.
Overall on my PC, Duke uses a 320x200 screenmode, so on my Amiga running that screenmode, its just as playable. Sounds are clear, movement is very good. Overall I am VERY HAPPY with the results.