Marvin, for you to understand the NRA rules as they come out every year or so you would need to first get a hammer and whack yourself in the head a couple hundred times , till all your common sense is gone...
Then understand that catalogued NOW doesnt mean, mass produced, /off the shelf/all the same/ in stock or out of stock until the next run . Like the Performance center PPC guns (which they allow for Distinguished) but not stock because their pretty picture was never in a "catalogue"
However a CUSTOM SHOP 1911, where you order ,the barrel,bushing/bull, caliber,safeties, checkering, guide rod,trigger,so and so on and then wait 2 years to get, is a catalogue gun because it has a picture in a catalogue. Go figure.....The rules/guns are listed on the NRA's competition website.
As far as an advantage of 6" over 5" accuracy wise none (if your gun is built right) a little more muzzle heavy and an extra inch of sight radius.
However if your eyes are good thats not an issue.
I believe the big reason the average scores for distinguish may have gone up a bit since the 6" was allowed, is the fact your shooting the same gun for the Dist Match that you just dialed in, on the open match 5, a couple hours earlier so not much of a sight change.Or at least your confidence is up and you dont look at your target.
There are probably alot of guys who have 5" guns that they would sell, now since they only use their 6", so you might find one easier.
Some of our young guys bought STI's they seem to shoot good enough for them , at least they were available, and at 1500. or so, you could always get one tightened up if it needed it, at least there usually in stock somewhere.
Dont get me wrong Any of the S/W PPC guns would be great shooters, but the last 6" I saw on a auction site went for over 4 grand. I have older Springfield guns and they shoot fine, but now its a 18-24 month wait.....Good luck, Bob