David's vocal range
 

What was his vocal range in the 80s/90s?

dude your questions are funny.

I would say it was up to the C of "ooahh, livin on a prayer!!" . :)

It was up to at least the Eb of the Prayer key change.

However, he can still hit at least a D# (the highest note on the same song after it being tuned half a step down).

It's really difficult to judge what he can actually hit, given how much of playback there is in those backing tracks, same with KTF. I think his current vocal range is much better judged when he sings clears harmonies, e.g. Who Says, Scars, Saturday Night, etc.

Isn't Faith's backing vocals just the FAITH? I'm not sure it includes the higher harmony.

It is just FAITH, but it's quite high and David always sings on top on it, but we never really hear him (basically the same situation as Prayer), so it's not a good song to assess him, that was my point.

In which key are the harmonies he sings over the chorus of I'd Die For You? He pulled them off very well in Cologne 2013:

Ah, gotcha. If he's the one doing the higher harmony on the "know you're going to live through the rain" part that'd be a good part to suss out how high he can go. That'd pretty high but I dont know who does it pre Everett taking over.

(we know of course that Eb and D# are the same note..)

Haha, true, almost missed it ;-)