You could also check on the Natami website. It is a project aiming at building a modern 68k Amiga computer. The CPU is emulated within a FPGA and is 68040 compatible. I think I read somewhere that the performances where similar to a 100 (or was it 166?) mhz 68040, which is already quite impressive.

Obviously, the product is not finished and I don't know how much work would be required to run Mac OS on top of it.