That's not really a fair question or comparison -- even for the X5 for the X3 -- because all three detectors are like comparing apples to oranges. They all have completely different features and functions and they all have their strong points and shortcomings just like any other detector ever made, which makes the buying decision all the more tougher to make.
The very good news is all 3 of those detectors are exceptionally high-quality machines, so all in all, no mater which one you picked, you wouldn't get screwed or anything. But I think the main point you should concern yourself with is -- at least as far as the Tejon vs. the X5 is concerned -- is the manual ground balancing issue. And if you live where the soil is red clay or anywhere that contains highly mineralized dirt, how well a detector deals with that kind of ground should be the #1 issue.
The Tejon needs to me manual ground balanced every time, and hear told, the manual ground balancing is very finicky with the Tejon. If you're in exceptionally mineralized ground, this could present a major pain in the butt. With the X5, you're able to either manual ground balance or use it as a turn on and go machine (which you can;t do with the Tejon) that, like Tesoro's turn on and go machines, handles a lot of halfway-bad soil pretty well, but in the *exceptionally* nasty stuff, there are better machines to be using above both the X5 and the Tejon for better performance. But even there, there are other drawbacks you wouldn't be facing with either the Tejon or the X5.
Personally, I'd choose the X5 over the Tejon simply because it's a far more versatile detector because you get far more features that can handle far more types of dirt. However, for twice as many features, you'll pay twice as much.
All in all, I guess it all boils down to what you need (or even expect to get) for the money you're willing to spend, and whether spending half as much will actually work for you.
Scott