Plays great in FS-UAE on my plain macbook though, hehe
How about scenarios with large battlefields and many enemies. I played the OS4 ports for quite some time and found that once you get to those types of scenarios the AI really bogged down my XE/G4. I started using it on Windows, first on an Althon at 1.8 and then an Intel Core2 1.8 setup. It wasn't really much better with seriously long waits between turns, I think it usually worked that I'd play my turn, switch to the A1 and do something else and check back every 5 minutes or so to see if the computer turn ended.
It's definitely been at least 6 or 7 years since I played so perhaps the main branch and any subsequent ports have become much more efficient. If not I think a 68k version will need carefully selected or specially made campaigns that don't expect too much in the way of CPU time.