I have the rack mount version of the X7000 - the S700. I recommend not getting the X7000, especially for $100 - that's way too much because the first thing you're going to have to replace is the 2.8" Quick Disk floppy drive unit - they all die. If you insist on getting it, make sure the drive works and loads sounds before buying it. But it WILL die on you. And it will be impossible to replace.
Get the ESQ-1 and then buy an Akai s900/950 rackmount sampler or whatever for $50 - they have a standard 3.5" floppy drive and far more memory and samples. You'll have the best of both worlds then, and have 2 very useful instruments. The ESQ-1 has a superb sequencer in it also, so you can use it to write your songs, not just play sounds and the Akai samples.
Casio: FZ1, CZ101, PG380, VZ10M, SK8, SK60, RAP10, DP1 drums, DH100, CDP200, DM100
Yamaha: TX81z, TX802, SHS10, DTXv2
Roland: SH101, DR660, MS1, PM16, TR33
Others: Korg MicroKontrol, ES-1, Alesis MMT8, Emu ESi2000 & card reader, BCR2000, V-Machine