To me, even the 2000XL lacks some major functionality that I am used to. For me, I can't use anything older than a 1000. I mean, for drums, sure, I could use any MPC, for fully arranging a song, I would be pretty tedious on anything less than a 1000.
I would say a 2500
. Plenty of people who rave about how nice a sampler sounds don't have beats that sound good. I only know a few people who have picked a certain sampler for sound reasons, then upgraded to something more modern for work flow. All have had great sounding beats on newer machines. The 2500 has everything I need, none of what I don't. I have to say that I am not familiar with the 5000, but not really interested in a new MPC, thus not interested. I will never sacrifice functionality with sound quality as an accurate sampler doesn't sound bad, especially with good samples, more especially after being mixed down well. The people I know who love their SP 12, MPC 60, MPC 3000 combo tend to not like to actually mix their songs and want their sampler to make magical things happen. It usually doesn't.