Right now I have a Pure Energy 68/4500 and I'm going to buy an E-orracle. I'm planning on getting another tank and I will have 200 including shipping to spend. I'll put my PE tank on my Spyder Xtra for a fun gun.
Just use a HP preset. There's next to no point whatsoever in getting an adjustable tank for a cocker. (Or a Spyder for that matter.) As far as brand name, as long as it's one that's been around long enough to prove they aren't crap, you really can't go wrong. Get a X-fire, Centerflag, whatever.