So without me having to take the skins off, can anyone remind me what the standard mount size is for TJ front door speakers? Is it 6 or 6.5 inch?

pretty sure they're 6. installing 6.5s is no drama unless you make your own baffles for the doors. the plastic is soft enough that a bit of force can make new holes when screwing the speakers into place.

they re 6.5s
but you can install anything in there even something slightly larger than 6.5 or smaller 5s, as you will need to replace the plastic harness with a decent MDF panel.
thats a must do upgrade if you re expecting any decent sound at all.

Everybody needs a set of 8's in there.