Um, YES time stretch! It's in trim mode. Not only that, but there are 20 something presets you can choose to optimise your stretching for different kinds of sounds. The only thing the 404 has on the 500 is the hands-on effects section, and the price tag. Here's a list things that make the MPC 500 better than the SP-404:
* You can't even change the pitch of a sample on the 404!! That was a deal-breaker for me.
* The 404 only has a one track sequencer.
* You can resample sounds on the 404, but not while the sequencer is playing (of course you can do this on the 500. This also means that you can finish a song, resample it as one long audio file and transfer it to your computer via USB).
* The pads. Just look at them. The MPC has big, soft, playable pads, while the SP has crappy little buttons (can't remember if they're velocity sensitive or not... I think they are).
* The 500 can do two effects simultaneuosly, plus one compressor/EQ "master effect".
* The SP-404 can't sequence external gear.
* For portablity, I find the 404 a bit bulky. The 500 is slimmer and better shaped for carrying around in a bag.
* The 500 will take up to a 2 gb CF card, whereas the 404 is stuck with 1 gig.
* Flashing lights? C'mon.
* Press "12 Levels" on the MPC and you can pitch a single sample over a whole octave and play a melody with it accross the pads.
* The 500 has much greater depth in sample editing, with things like envelopes that can modulate differnt parameters.
* You can stack up to 4 samples on each pad on the 500, with velocity switching.
There's probably more, but I should get back to work. In short, I bought the SP-404 based almost soley on the fact that it ran on batteries, to replace my aging
Yamaha SU-10. When the MPC 500 was announced, I got one as soon as I could and sold my 404, and it was the happiest day of my life.