Depends on the PTR-91 and M1A matched up to shoot against each other. An short of a PSG-1 clone I don't think any G3 pattern rifle will outshoot a National Match M1A.
Since no one ever used or uses a HK91 action in NRA Highpower competition, I have never seen the two shooting the same game. I have taken my PTR91 out to my Club's "Old Military Gun Match", and the lack of a bolt hold open device rules out the HK91 as a competition rifle. NRA rules require single loading and this mechanism is not made for single loading prone, with a sling.
I have paper reports from an estate sale and one of them dates back to the 1950's when these rifles were all being tested against each other. Mind you the ammunition was ball, and that is not accurate at all. None of the service rifles of the period, that is FAL's, M14's, and G3's are all that accurate. Basically 4 MOA to 6 MOA groups. These rifles can be built into more accurate machines, but then they become target rifles, not service rifles.
I got my Distinguished Rifleman Badge with an NM M1a. Still have a thunderstick and shoot it occasionally. I am happy to state I shot it this month in my Club's 100 yard reduced match, and shot a 96 out of 100 offhand. I have not totally lost it! Prone rapid fire was a train wreck. Shot a 188 prone slow fire, one seven out the top. I would hate to have to hump the thing all day, it must be around 12 to 15 pounds with the heavy barrel and lead shot in the buttstock. Sure is accurate, but it is not a service rifle. It looks like a service rifle, but it is not a service rifle anymore.