Wakal, I wish I could come. But even if I did I get the feeling that the fur hat would get really warm in Texas.
Probably in better answer to the first poster, from what I've seen the experience level of the shooter matters less than the type of match being shot as far as equipment goes.
If you are shooting in some of the USPSA matches you can see some pretty tricked out guns. I got to play with a really nice JP Enterprises Race AR a little while ago. It had a muzzle brake that looked like it came off of a 105 mm howitzer. It had 2 optical sights, a Leopold on the flat top, and an Optima on the float tube, but kind of on the side so that you would mount the gun on an angle for close and fast shots (I can't say I liked that much). Recoil was non existant, and it was supposed to be a 1/4 MOA rifle. Now if you are shooting in the WC3gun then that wouldn't be allowed as they have equipment rules that try to keep the guns more realistic.
Most common guns in our local matches are ARs followed by AKs. The AKs really aren't at that much of a disadvantage as our longest shots at our local range don't go much past 200 yards, 300 if you really move stuff around. Some of us use FALs or M1a. There will also be a scattering of things like the SKS.
We have folks show up with all manner of rifles for their first match. A really good feeling is to step up to the line with your $600 FAL built out of spare parts and beat the guy with the JP. It is the man not the machine that wins.
I have a Cav Arms AR, but I have not played with it much yet. So I don't have a real strong opinion on it one way or the other yet. I don't think light weight is that much of an advantage. Having a bit more weight out front will steady you for the long shots, but you may not swing as fast on the CQB style stages. Depends on what you are more comfortable with.
As for shotguns you will be able to hang in there just fine with your Winchester. It is a fine pump. Pumps are a bit slower. I'm a pumpgunner myself, but I will be the first to admit that if you take 2 shotgunners of equal skill, and put them on a speed stage, one with a pump, one with an auto the auto will usually win. At the higher levels you will see almost nobody run with a pump unless they are very seriously minded (like Andrew Wyatt was talking about) and then they will use their duty or home defense gun.
I usually beat most everybody at our local matches in the shotgun stages, and that is with my pump, but I have practice a ton with it. When I go to bigger matches and run my pump I will still finish well, but anybody with equal skill but an auto will take me.
Your Glock 19 is a fine gun. As long as it fits you and you practice with it you will be fine. If Glocks are your thing you may want to take a look at some of their Practical models. I'm a 1911 kind of guys but some of my best buddies swear by their Glocks. And pistol is my weakest weapon in 3 gun, so I get beat by those damn Glockers enough that I can't make fun of their guns.
