> 1) If time/space/memory were no option, what settings/compressors settings would
> (most likely) give me the best possible zip compression on my rom set?

There are no settings. Ben Jos tried 255 different external packers...Results vary.


> 2) I'm concerned that I might somehow make my zip files incompatible with the
> zlib used in MAME? Is this even possible?


No. zipmax creates 100% standard zipfiles.