"Back in the day" when I competed in NRA Highpower with the NM M14/M1A before switching to AR15's, we considered the life of a NM M14 barrel (non chrome lined, of course) to be about 5,000 to 6,000 rounds max. That's in the context of NRA Highpower when out of every 60 or so shots, only 20 were fired "rapid fire" and that was 10 rounds in either 60 or 70 seconds. If you shoot much rapid fire or long strings of fire when the barrel is hot I'd expect less.
Personally I think the "loaded" package doesn't offer much for the money. You can stamp "NM" on a turd but that doesn't mean it's worth anything. If the "NM" barrel on the "loaded" M1A is the thin profile and not heavy, it won't make a lot of difference to improved accuracy in my experience. Similarly, the "NM" trigger may or may not be really match quality, the "NM" flash suppressor is just tapered on the inside, etc. If it's not properly glass bedded, gas system unitized, etc., it's not a true national match quality rifle. NM sights, properly, are hand-fitted/lapped in by a gunsmith, not just slapped onto the rifle and I seriously doubt any fitting is done to the "NM" sights on the "loaded" package. It might shoot a bit better than a rack grade but not $500 worth, IMHO. If you're just planning on doing a bunch of fun shooting, I'd consider getting the standard walnut and paying a good gunsmith to glass bed it and tune the trigger. You may be surprised how well it shoots after that, and it won't cost much to have that work done.
Hope helpful,
John