And you should be aware that there are differences between the classic series and the Ultra series. If that e4x is from the classic series, it will run slower than the Ultra, and won't be able to run the "beat munging" feature of the 4.x software. Might also not have enough system RAM for loading particularly large sound banks.
[how much slower? well, depending on the function, half the speed... so something that would take 2 minutes on an Ultra might take 4 minutes or longer on a classic... now, I'm taking really processor intensive stuff, like transform multiplication (better known these days as convolution), which can take quite a while depending on the length of the samples being processed... obviously, simpler stuff shouldn't take nearly as long or have quite the speed difference between classic and ultra]
If all you're interested in is live playing, then the speed of the processor isn't as critical (although it can affect how long it takes banks to load) because you won't be doing as much sample mangling in the unit.
The short version of history: First came the original EIV, and it's little brother, the e64. These are unofficially referred to as the "vintage" range of Emulator 4 units. Then came the "classic" range, with the e4x (which could be upgraded to "turbo" status, becoming the e4xt). It had a smaller brother, the e6400, which had most of the features of the e4xt as optional upgrades. The e4k fits in here somewhere as well. Then came the Ultra range (which is clearly distinguishable by the word "Ultra" on the front of all such units). Again, the e4xt Ultra was top of the line. The e6400 Ultra was a stripped down version, but could be upgraded to the full e4xt Ultra stats. And they added an extra version, the e5000 Ultra... which has some better starting features than a bare bones e6400 Ultra, but couldn't be upgraded to the full e4xtUltra specs.
As mentioned, marked differences between the classic and Ultra models (and I won't even get into the "vintage" units, as they had a completely different main board design, and can't take most of the upgrades you might find of classic or Ultra series units). Classics could have their main system RAM upgraded and run the Ultra 4.x version software, allowing them to get almost all the same functions as the Ultra, but slower and missing the very processor intensive "beat munging" (cutting up a beat loop so you can screw around with tempo without compromising pitch or sample resolution, among other things). However, the system RAM upgrade for classic units only takes you to half of the system RAM of the Ultra units (classic maxed out at 4Mb, I think, while Ultras had 8Mb). System RAM will affect the maximum size of banks you can load (as the preset data goes into RAM shared with the OS, while the samples go into regular sample RAM)
Don't know if any of this will help you, but there you go...
[later...]
Oh, and there's the whole situation with FX (careful now, this gets even more complicated). The e4x (e4xt) classic had a basic 24-bit effects processor (nothing fancy... in fact, you'd be better off with an external FX unit) as standard, while that 24-bit FX was an upgrade for e6400 Classic units. When E-mu went to the Ultra series, the 24-bit FX came standard on ALL models. Then E-mu introduced a newer 32-bit FX card, the RFX-32. Powerful as all hell, but has serious software issues. Classic units can't install the RFX-32 at all. The Ultras can... but you can't really run the top EOS 4.7 version because it causes things like random noise bursts from the RFX-32. Again, probably less trouble to just to have an external FX box (although there were all sorts of really neat features promised with the RFX-32... but unfortunately, at around that time Creative Labs decided that E-mu should stop all design, manufacture, and support of professional hardware gear and switch over to just software and sound cards for PC... yes, we're all very bitter about it
)