Sorry I didn't reply sooner. I didn't see any notifications about new posts to this thread until today. In the end, I got the 7100 which, to me, seems super bright.
I only have two minor negative comments about it. The first is that it struggles sometimes when there are large patches of darkness with a gradient on screen which look clumsily pixelated, but this is very occasional so not a big deal.
The second (and something I've still not worked out) is that the brightness takes noticeable jumps upwards and downwards when the image changes to a much darker or brighter image. I think this is to do with the iris (but I know little about these things) and it's trying to make the dark images more viewable by increasing brightness, and dropping the brightness back down when bright images are shown. I appreciate what it's trying to do, but it's very clunky so you notice the obvious steps up and down in brightness which are distracting. I haven't worked out how to stop it doing it as I'd prefer not to have that.
(One other note is that I use an Xbox Series X for all my projection and, sometimes, switching between different apps like from Netflix to Amazon Prime seems to confuse the projector as the screen goes blank for quite a while (even though I can hear the Xbox is still running/responding). No idea what that is about. Probably more to do with the Xbox than the 7100.)