The wylde is a short thoated chambering for the .223. The reason for this is it sets the bullet closer to the lands when it chambers. Less jump = more accuracy. The Wylde chamber really comes into play when you are launching 80 grainers that are sized longer than 2.500 OAL. I think the Wylde is pretty standard on RRA rifles now, and they make a GREAT rifle. I have not heard about any problems with the wylde chamberings and if you are going to be shooting long range, over 500 yards, the wylde will be an advantage. Of course you have to look at the twist rate too.
The wylde chamber is a compromise between the 5.56 and the .223. Most RRA rifles are a 1-9 twist. Mine is fabulous, I couldnt ask for a better rifle. Im currently building a .204 that will have a RRA lower and 2 stage trigger.
If you get the RRA NM rifle, it will come with a SS 1/8 twist Wilson air-gaged barrel. If you're going to shoot in matches, that's the one you want. The barrel is free floated, 2 stage trigger and match sights. RRA is by far the best off the shelf NM service rifle you can get. Just make sure you get a good Turner sling and a balance weight for the butt stock. It will help balance the rifle for offhand.