I've just upgraded from 2.7 to 2.9 (missed 2.8 due to not wanting to upset active projects at the time) and did a pano render as a test to compare.
I was a bit concerned as it seemed to be a slower render so I checked that RTX was off etc and then opened both the 2.7 and 2.9 renders in Afinity Photo to compare.....
WOW! panos now render at 16k x 8k! instead of the 8x4, thats why it was a little slower. It maybe that the change happed in 2.8 and I missed it.
Is there a complete change log for 2.9 (and other versions for that matter)?
Here's a quick comparison between the 16k and 8k: