Is there any real difference, in either performance or quality, between these two loads?

The reason I ask, is that the XM193 is praised so much here, but the Q3131A is available locally in my area, where the XM193 is not.

TIA

Cant go wrong with either.  I buy whichever happens to be the best deal going at the time...

Both high quality loads.  XM193 has more flash and few more fps (less than 50). Q3131A has shiny brass.

Quoted: Both high quality loads.  XM193 has more flash and few more fps (less than 50). Q3131A has shiny brass.

Which means the subject of your attention will be MORE DEAD with the XM193 vs. the Q3131A, eh?  :)  (J/K)

BOTH SHOULD BE BANNED!

The basic answer is if Q3131A is available and XM193 is not, then buy what you can get.

The difference between them is that XM193 has 100+ fps advantage when tested side by side with a chronograph.  Q3131A has a bit less less recoil and muzzel blast.  Both are comparable accurate, but a slight edge to XM 193 in three test rifles.

XM193 is generally regarded as the gold standard, but both are excellent.  Get what you like and, most importantly, practice and be proficient with whatever you choose.  The most important of the shooting combination is the shooter.

One other consideration, get a cheaper cartridge for general blasting, use your choice of XM/Q3131A for self defense, sighting in, but do practice for proficiency with it, and reserve a stock for a rainy day.