Well, for starters, you're asking this on an explorer forum, so go figure the opinions, haha. And secondly, your question is trying to compare apples to oranges. They're just two separate types of machines altogether. The X5 will have a much less accurate ID at depth. So while you may get "clicks" (thus some people would argue you've gone just as deep as an explorer), yet you have to factor TID into it. And the type hunt environments you intend to go to, also play a role in this. Ie,: perhaps you are in a relic-mindset area, where you simply intend to dig-all anyhow? And soil type plays into the question. The Explorer will handle more soil types, IMHO. There might be a place for the X5, but I can't say for certain. The only x5 I ever got to see in practice (pitted in a junky hardpan parking strip against a few other makes and models, when it first came out) was lacking terribly. Everything sounded the same. Of course, we were in an arena where we wanted to (gasp) loose foil, etc... It was more of an "under bleachers go for the copper/silver" type hunt environment, and I found the X5 to be seriously lacking, overly senstive (no matter how we tuned it), etc... However, shortly after that, apparently Troy Co. did see that it was too sensitive, so they did a modification to all the ones coming off the assembly line thereafter. I have not seen/tried these series II type X5's. The X2 (the X5's predecessor) does indeed see through and around iron better (so long as we're not talking super deep) iron better. So for example, it would be a better ghost town machine, IMHO.
So as you can see, depth isn't the only issue, and even to the degree we all want to know how deep a machine goes, there's multiple layered factors to lay on top of the depth question.
All in all, the Explorer is pretty durn versatile, and .... considering the "power house" that it is, it holds its own in the target-separation and averaging department of capabality. If you put on the a 5" coil, you can do pretty good in and amongst iron. But there will be 2 filter machines that will out-hunt an explorer in some iron-riddled environments (with the depth question aside).