Xavier is in a wheelchair. Magneto doesn't get into fist fights. Not sure about you but I would perfer a down and dirty Cable that gets physical.
Also, if Cable is going to lead and/or star in a movie you would expect the studio to do after an actor that can be sold in the same way Jackman has carried X-Men.
Personally I'd go with someone like Armie Hammer. He's 6'5. Can act well. Has a deep voice. Can probably pull off this kind of Cable:
If not him at least someone similar. If they can find a guy like that in his 40s instead then gravy. If not thirties works too. Aging someone up is easier than aging down anyway.