If you are looking at the 3 vs 4, these are the things to consider: the 3 has a shorter blade (duh!) but it is also 1/8" thick. IIRC, the 4 is 3/16" thick... So the 4 is slightly longer, but thicker as well. If you want a great slicer, go with the 3, since it's thinner. If you want a brute-tough knife that will handle a lot of punishment, go with the 4.
However, at that price point, I would highly suggest you take a look at scrapyard knives. I have a SYKCO 311 and it is hell for stout. It does anything I need a small knife to do, and it performs like a little bit larger knife. You can really beat the crap out of them. The steel is remarkably tough, they take and hold a screaming sharp edge, and they are very lightweight... Just something to consider.
I love Esee knives, but if I was spending that amount of money, scrapyard would get my vote.