Looking at the mess of various accelerator cards that were made for amigas. I see some 040's clocked at lower speeds than some 030 cards. Would there be any gain to an 040 in that case, or is it better to just go for the higher mhz ?
040 is a totally different beast.
The 68030 is merely a higher clocked 68020 with a bit of extra cache, the 68040 has newer instructions, more cache, has Pipelines etc.
68060, is a totally different beast, being Motorola's attempt in to the Pentium world but lacked the pipeline of the pentium, and then they went to PPC.
SO to cut a long story short, even though its lower clock, 68040 will run faster than a higher clocked 68030 because the 040 is more highly optimized.
68000 (68010 - Revised 68000)
68020 (68030 - Revised 68020)
68040 (68050 - Cancelled)
68060..... (68070, made by Philips, not a Motorola CPU).
68080 not even put to design board, but would have been a P6 architecture (Pentium Pro, which was used as a foundation for Pentium M).