New versions of MAME for 68K are unreasonable because they will be extremely slow even for pre-1984 year games, which worked on the Triumphs version much faster, because as FAB said the emulation gets more accurate, thus slower. Old sources of MAME are available and for weaker hardware they are usually recompiled instead of the new versions. On the N-Gage for example the EEMAME is port of MAME 0.37b7.
New recompiles of old versions of MAME for 68K may be usefull where parts of the code can be optimized with unrolling loops, inline assembler or other tricks (may be even using the Amiga hardware). MAME for 68K played only some games at acceptable speed on AGA Amiga400 68040/25 MHz, but on 68060 with GFX card it will be much better.
On AmigaOS 4 the version is good and more recent games are playable on AmigaOne 750GX/800MHz, if not all the best. Small problem on the AmigaOS 4 port is the lack of AmigaInput support and that some ROMs because it is old version are hard to find, but the best games are supported there. Legend of Makay, Ninja Warrior, Commando, Robocop, Rygar, Outrun, Turbo Outrun, Shinobi, Contra, Escape from Planet of Robot Monsters and all the other great games are playable.
