Yes, well, it wouldn't run at all if Altirra wasn't emulating the XEP80 to at least some extent.
I was hoping someone with real hardware would chime in. I take it everything worked fine, aside from the general, relative slowness that the XEP80 driver is known for?
There were certainly screen glitches and bugs that required refreshing the screen but nothing that irked me that much. It's been 20 some years since I last used it. I just recently found the old amber composite monitor. I do remember that I had it hooked up to an A/B switch (to the video out on the Atari itself) and always had to fiddle with the screen size controls to get a good display in 80 mode.
Not much help when it comes to Altirra but when I dig the XEP out again I'll test it.