I just bought an e6400 ultra with 128mb ram and 128 voice expansion, scsi disks etc, 330 euro. (just hope it arrives now

the only thing I'd wanted from an e4xt was the second midi in/out, that'd have been great for me but I'll survive with a midi merge box on front of it I guess.
Consider shopping around for a much lower price, they are out there..
I own a yamaha a3000 already. I know you asked about the 4k but what the hell. The a3000 is pretty nice, kinda slow to load and save and do stuff like normalization, but it sounds excellent, very clean, and the timing isn't too bad. Its full of fx too, and I actually use it mostly to route the input signal through the fx and out again, so its a multifx box. The knobs are well known to suck on these (the 4k/5k may have been improved). they cost around 100euro but they are brutally heavy so shipping is gonna cost too. I cut the fan out of mine, so its totally silent. Been running a few hours a day like that in a rack for years now, no sign of any trouble (or any noticible warming)