I have an A4000 in an Elbox Power Tower, with Repulse soundcard, FastATA, Mediator 4000, Voodoo 3, TV card, Cyberstorm 060/PPC, running OS4.0.
I also have an AmigaOne XE/G4 running OS4.1.
The AmigaOne is used every single day, the A4000 is switched on only occasionally. The AmigaOne is just way faster, and nicer to use.
I probably should sell the 4000, but it has too much sentimental value... and I still like it, its just not as nice to use as the A1.
So, basically, I say go for the SAM.