Ive never used a cn700 based machine, but based on my experiences with a 1ghz pentium3 (which is probably a little faster) (win)uae will be a little hit and miss. You can tune it to work a bit better on lower spec hardware, but at a compromise to compatibility. There's definately some fun to be had with uae on such a machine, but it'll require some juggling of config files for different softwre so probably not a great choice if you want to create an "all in one" amiga type system.
Assuming it works at all AROS should be ok on such a machine, but you'll have to make a few compromises with what you do (720x576 or thereabout max video playback, same boat as winuae for 68k amiga software (only a little slower again than winuae) and so on and so forth). Id personally probably chose a different hardware platform for such a project, but it should be an okay-ish, experience. Depends on what you want to do exactly.