all the E4's (e4 platinum, e4xt ultra, e6400, e5000) all run on EOS, the same OS, so crashing shouldn't be due to what hardware piece you own. the latest version of EOS, 4.61, seems fine in terms of stability. i'm even running version 4.70, a beta version of a new OS never officially released (although my brand new E4XT Ultra came w/ it pre-installed?)
about upgrades, i'm not TOO sure, but i thought any e4, even the E5000 could be upgraded to E4 platinum (every option imaginable) status.
someone should verify this though...u could ask emu too of course