I used to have 2500 for 2 years and i can see why 8800 can seem little strange.. i didn't like it at the beginning, first week i was little disappointed because i couldn't make anything fast. but ofcourse .. it is so much different. but right now i love it, i have been using it for 8 months and i feel like i can't go back(although i have mpc 500, i had a good deal).. this has OS 1.00 and no single bug or error had bugged me since the day i purchased this machine.
I'm working without quantization so i haven't found any quantize problems yet. Pads are little different, they response different way, but i got used to it. Best thing in this machine is the sequencer and the work flow i think.. it's really fast when you learn a little.. it's nice to sample in through 12bit effect (which has very nice options for making your sound).
Overall effects are so much better, resampling is easy.. Choppin is way more better than in 2.5k, i'm not sure if 5k has non destructive choppin but mv has it, that was a great thing when i was coming from 2.5k. i can't even explain it but after little playing with this machine i wondered why i hadn't bought this before.. and no rza or jermaine dupri didn't help me buy this.. i think i had a little doubt because they have this

but yeah.. i could manage with mpc which has 2mb ram but i'm using this cause i feel like i have so free hands. although my beats take diskspace about 5mb each.
so i have to vote for MV although i haven't tried 5k, only read about it.