Really interesting stuff. I've used a single, 70s 810 with my SVT head for years with no issues. The "you better buy 2" marketing hype totally makes sense.
I've got a single SVT 810 80s cab and a Skunkworks SVT head...actually the one that was loaned by Ampeg as the stage amp for Woodstock II....even still had mud on it when I got it.)
I've also got a pair of the current Orange 810 cabs (squareback; 4 Ohm cabs,) which I really like. Only problem is that you cannot run an Orange AD200B head down to 2 Ohms!! So, you cannot simply chain two 810 cabs to one head if you wanted to.
Fortunately, that's not the way I use them. I'd got the second one to use with a separate head for 8- and 12-string bass for overdriving/dirtying up the highs.
But I find myself usually only needing the 1x15 cabs for most gigs. Not a lot of call for the big rig.....but the cabs make nice coffee tables when put horizontally
I got crazy great deals of each of the 810 Orange cabs, so they were justified. One Orange dealer in a very small town could not sell the 810, so he traded me for my two Orange 410 cabs + $300 (cabs I really didn't like, with the horns and no attenuators.) The second 810 I got new for around 55 percent off list....too good to pass up.