A 68060 version should be better than a 68020 version for the 68060 if the compiler can...
1) schedule instructions for the 68060
2) avoid missing trapped instructions (64 bit integer instructions only if no fp)
3) prefer instructions that work in both integer units of 68060
Most compilers generating 68060 code will do better with 1 & 2 while few understand 3 even though it can speed code by up to 2x alone. I would say a 68060 version is still justified for reasons 1 and 2. Separate 68000, 68020, 68040 and 68060 versions would be nice for stable major releases.
This is the theory, indeed. In practice, however, I've never seen any real benefits in toggling between 020, 030 040 or 060 targets when running the code on 060. Even the case 2 is handled by Cyberpatcher.
In most cases the C compiler produces adequate results as long as you tell it to produce 020+ code. Back when I was still into 68k I used SAS/C and gcc and checked out the code produced for performance issues. It was quite awful. Even when I told gcc to produce code for 060 it would still use the instructions that would get generate an exception. The generated code had no sensible scheduling. If I really needed the speed I optimized the critical part(s) by hand.
