I have been poking around on the HobbyKing site, just to brush up on the items discussed here - my initial reaction is that a 54-60 oz model should be fine on a 4 cell setup. One combination that we have flying here is the Turnigy SK3548-900 on 4 cells. Plenty of power with a 12-6 for a model of that size, with adequate headroom for a governor mode ESC to do its thing. It will also handle a 13" prop and the extra current that it requires. I have also been using my Twister as a 4 cell testbed with a 900 Kv motor and a Phoenix 45. Weight is probably right around 51 oz, like it was with a 3 cell setup, and the power is way more than needed. The 3 cell/1100 Kv setup drew an average of 3000 mah for a 'full-pattern' 5:30 flight. It appears that the 4 cell/900 Kv setup will be under 2500 mah (maybe even less) for the same flight (both using a 12-6 prop).
If you really want to do a 5 cell, I would opt for a motor with a lower Kv -- in fact, I think even with four cells and a governor mode ESC, you could get by with a Kv of 750 - 850. You could choose a C4250-700 or even an SK4240-750. There is also one of the 'red & blue' motors - a 3548-850 that I've been thinking about giving a shot.
I would also like to point out that the SK line is a step up in quality over the "C" line motors - they have better magnets, better bearings and (in the 35xx size, at least) larger shafts. That said, I have flown the Twister with both an SK3548-1100 and a C3548-1100 and there is no discernable difference in the way they fly on the Twister. The main considerations there would be if mounting it in a full-fuse, that you get some cooling over the motor and battery, whichever model you choose - I can tell you that it is possible to cook a motor if there is no cooling and as soon as I get it re-wound, I can tell you if the Kv was a little too high or not.