Hey man-
There are ups and downs to every MPC out there, even the 4000. (If you can afford it, it's the shit... God, it's the shit...)
Here's the real deal on them:
Mpc 60: Nice gritty sound, (still not an SP 1200) only 26 sec of sample time when fully expanded (if you can even find the sample ram now.) Get the OS upgrade, don't fuck with the SCSI update, shit's worthless and the floppy aint that slow.
Mpc 3000: Every major hit you've probably heard in hiphop has had drums coming from one of these for a reason. 16 bit, but the A/D on this thing still is RAW. Makes a 2000 sound like a toy. Comes with the 8 outs, and has a built echo mixer. (So does the 60!) The 4 MIDI outputs makes it really the hub of your sequencing enviroment. Plus it can hold twice the amount of ram than a 2000. (Try 6 minutes of stereo sampling...) Until the 4000 came around, this was the big daddy, and shit, you can still pay $1800 for a USED one...
Mpc 2000: Very nice alternative, especially if you're buying second hand. Waveform editing was added to make chopping samples faster, but you gotta load the OS everytime. (Get a ZIP drive homie!) Can hold 99 sequences in memory, but you only have 1 program per sequence. You have to add the 8 outs, but you do get 3 mins of stereo sampling when blown out. (also, only 2 midi outs... wtf???)
Mpc 2000xl: Even nicer still, but just not a 3000. Still only has the 2 midi outs, but the flip screen is back, timestretch is there (I don't know what you guys are talking about, you must be trying to stretch like 30 sec. samples or something or not have enough ram, mine never took too long....), and the ability to run 4 programs simultaneously for beats. You only get 64 sequences & tracks now, and you still gotta buy the 8 outs. Probably the MPC you'd get if you have $700-$1000.
Mpc 1000: Although I haven't used one personally, the lowdown I've been hearing is that they sound even more plastic than the 2000xl, now putting in the ASR-X category. (C'mon, you guys with those boxes know what I'm talking about- rubbery ass basketball kick drums and weak D/A converters!) It does give you effects, but honestly Akai effects are not something to write home about. It does give you 2 sliders now for manipulation, but still, it's the sound that matters, right?
Mpc 4000: Ok, first off, I'm going to say this: It ain't for your average mu'fucka. You really gotta understand A LOT about sampling to take advantage of this thing. People swear up and down everyday that there's thousands of "bugs" in it because they expect Mpc 2000 operation, and it's more of a rack sampler. I have a S5000 so I'm right at home with the purple guy. Some quick specs:
-Reads EVERY Akai sound. (From S950 up- that INCLUDES the MPC 60)
-24/96 operation. 29 minutes sample time @ that sample rate in mono; 14 in stereo.
-6 Q links
-128 sequences, 128 tracks in each sequence with 3 types of sequencing. (Yes, you can now edit velocity, duration, etc.. in a drum roll fashion)
-The sequencer has the feel of the 3000. Now you'll be touching the pads of it more than your girl's ass...
-Built in effects, twenty-fucking-one filter types, turntable preamp, and XLR ins/outs.
Now, with that said, if you never make ONE dope beat from it, the sheer size of it alone will get you pussy in the studio. (If it doesn't, you probably couldn't get none anyway... HAHAHAHAHAHA)