I think the variety of butt caps are mainly due the variety of asthetic taste we all have . They can come in cork, rubber, metal, wood/wood burles, etc and they pretty much do the exact same job. Only difference is in how they look so Mojo, if you like cork, then a butt cap made of cork is for you. I like a metal collar with rubber bumper...heck its pretty much all the same!
While I am making a post, Carpman...any reason you wouldnt consider a 3113??? I havent fished the other 2 models but my 3113mb has been a delight for all the rivers I fish (chehalis,vedder, cap, seymour, thompson, stamp, etc).
The 3113 is a very limber rod with a nice even bend from top to bottom. It has a soft tip, great for casting a pin, and a strong back bone too. Its soft tip makes it nice to play even a 3-4 lb cap coho and its back bone makes it capable of subduing chums and big whites too. One of my most memorable battles on my 3113 was a 9 lb summer run taken on 4lb test! Simply awsome! I would highly recommend you consider that model too.