How strong is the In-Between gate, based on its appearance? Just strong enough to hold back a wave of Ubelites or powerful enough to turn back a drow army?

Don't forget that there's a tall spiral staircase ("even a hearty man would feel winded") and not a whole lot of room. This is baseless conjecture, but I don't think In-between was meant to support an army, either, considering the cirumstances of its construction, and I think it mostly exists to help PCs realize how much physical distance there is between Upper and Lower.

Edit: I just realized I haven't answered your question, but I don't think an answer would be of any practical use anyways.

Strong enough to hold out a mob for a time, probably. It's just a big metal gate.

Would it be reasonable to say that the link between the security of Lower's gate and Upper's safety is still strong? I remember back during the Lower rebellion/Council, a lot of people were worried that drow would invade Lower and sweep through Upper, and that the Tigereyes were hired to man the Lower gate so that Upper wouldn't risk being overrun. If it's just a big metal gate, then it wouldn't do much to stop a reasonably determined force, so do reasonable figures concerned with the security of Upper look at the various factions in Lower as necessary buffers, or aren't they concerned about that?

That might be a FOIG. But maybe this is a hint: Tiger Eye rebellion?

Complete FOIG.

FOIG

It's not like we're fascists or anything, but. . .FOIG.

FOIG!

Yay now I fit in! :D

No, you guys are fascists.

Thanks for the information you did give me

Next time I will read the rules about posting in this forum before I proceed to post.