Duke 3d works better with shapeshifter (mac emu)
Maybe coders are too used to fast winuea / ppc, to write fast 68k code
Nope, it's just you being too lazy, not having done a better port yet :-)
A few things to consider:
-Mac version was a commercial port done with big money
-Original code release had LOTS of optimizations (read: X86 assembler code) - this had to be re-written as C to get it working on other platforms
-Amiga versions are free ports of freely done linux versions
-On linux no-one cares that much about how well it works on slower systems
Indeed there's space for lots of optimizations. Please tell us when you've finished doing them :-)