I actually think that Goretex socks could solve the gap issue, as mine at least are fairly high, but to me at least, it feels like killing a fly with a cannon ball. Unless the conditions are such that you actually want goretex socks for what they're made for, my inclination would be to go with some sort of gaitor --- or wool socks. At least in my experience, mosquitos find it challenging to bite through reasonably thick wool socks.

I use a different approach to the "gaps in coverage" issue --- in fact, my shirt is thin enough that they can nail me through it. For me it's a matter of keeping on the move while on the trail, being careful to select a windy or for whatever reason low bug area to take a lunch break, and then being efficient at minimal chores in camp and then climb into the tent (and stay there). It really depends on what your hiking style is, however, and just generally the nature of the trip.