You have to make your choice. You say you "don't want to loose coverage", yet you want something better for in-the-trash (iron, etc...). While it's true that the 6x8 has more "coverage" than the 5", yet the 5" is going to afford you better separation. You can't have it both ways. The 5" will separate better (less items in the field-of-view for it to potentially "mask" on), yet the 6x8 (which, yes, is better than the 10.5 on "separation") will be more prone to masking.
You gotta make your choice. Can't have the best of both worlds.
I would go with the 5". And here's why:
a) The 10.5 on the various explorer's, FOR THE DEPTH DEMON THAT IT IS, is still pretty durned good (considering the power-house that it is) in separation aspects. It's got a sort of "averaging" of targets that , going slow over suspected targets, you can often get a peak (in audio) of stuff trying to peak through. And yes I realize that in the "foot-print" of a large coil like the 10.5, and if you have a very trash/iron ridden site, that it's no longer a matter of a conductor trying to peak through a single nail or whatever. Because there can be MULTIPLE nails within the footprint of the 10.5. But all-in-all, if you're just hitting a single nail over (or next to) a coin, the explorer's, even with the 10.5, give you a fighting chance (with proper wiggle, and slowness) to get peaks.
b) So therefore, if I find myself un-satisfied with that (for a really bad site), then the mere definition of such a type site, means I'd want the most optimum guns. I mean, in-such-sites, "coverage" is no longer an issue, so why oh why do I care to have the added "coverage" of 8" vs 5", when my new objective is "trash-see-through/around" ?
c) I don't think there's much depth difference in the 6x8 versus the 5". And to the extent there IS a depth difference with the slightly larger coil, you still have to take into account, that any conditions where you've had to reach for the smaller coil, is often a place where "depth" is an issue that's thrown out the window. You're in places where your primary objective is see through-around. And you have to compromise on not expecting the depth that you could other wise get. Because again, you can't have the best of both worlds.