If you buy a NG OS4 machine under the guise you'll simply be able to "plug and play" all those oldie fave games and demos you toyed with 20 years ago on legacy hardware, a fool and his money are quickly parted.
I love both my SAM and my MOS machines, but to think of buying either to get a hassle free experience of your youth that you had 20 years ago on your old A500, you'll be sorely let down.
The smart option would be to grab UAE and OS4 FE and give it a whirl, see if you even like the OS4 experience at all to begin with.
Anyone telling you that you can sit around all day long, downloading old (legacy, 68k) games and demos on a NG machine and just unpack them to RAM and run them without the buffer of an emulator (yeah, emulating an Amiga on an Amiga type of deal) - well, you're simply not being told the truth. And I can say that as the owner of a pre-order SAM440 from 2008, 7 years of experience with it.
Thankfully, I had no illusions nor desires to run oldie SW on the SAM, and I love the machine for what it is.
I don't wish to badmouth any NG system - they are super, as long as you realize what they can and cannot do. I question the sanity of anyone buying a $3000 X1000 with dreams of running old games and demos, many - if not most, would require you running an emulator on the machine just like you would have to on a $150 Wintel PC.