and infact i am rite now choosin between am MPC-5000 or a MV-8800 and as it seem rite now ive leaning thowards the MV.. as the sound is special in the Roland products.
I definitely would advise you to go with the MV, I've got the MV-8800 now and I'm loving it so bad, that I often fall asleep on it man! Pads are sooo damn comfy!
I've dropped the idea of also buying the MC-808 though, as I don't have that kind of money at the moment.
I've looked into the MPC5000 myself before buying the MV and did not like it (better).
I've played around with it for about 2 hours and it's cool, you can do neat stuff on it. 'It works'. But it's sort of outmatched by the MV in most areas.
Sure.. the MPC5K has a better synth, but if you want a good one, you'd be better off to just buy and use a separate and real synth anyways. Having said that though, the MV-8800 synth works great for me. Even synth solos and so on. In case I need more of a real synth, I'll use a MicroKorg. Cheap but worth much much more than they go for, for real!
The HD recording on the MPC5K is better as it's 'true HD recording', but it's not going to be anything you'll really miss out on, as the MV can bounce audio to tracks. The MV uses it's RAM to save song stuff, but with 512MB RAM maxed out, there won't really be a lot of cases where you'll run into problems at all.
The sound on the MV definitely rocks, but it rocks even more when you dive into mixing your tracks the right way. There's a whole lot of options there. I also have to say that I found the 24bit sound on the MPC5K way too clean sounding, not really that punchy and crunchy as the good old MPCs either. I guess the 'mpc3500' error in the manual sort of explains this as the MPC5K is based on the MPC2500, not the MPC4000.
Anyways, there's so many features and options on the MV that you won't really need more sampler-wise, except maybe more soundpatches, a huge collection of vinyl to sample from and some live instruments.
(The sounds that come stock with the MV-8800 are great, but I never use them 'clean'... layering them like crazy instead.

)
Anyways, I definitely advise you to try both machines out if possible. I think you're going to like the work-flow of the MV a lot more though as you're used to the SP-606 as well.