The 7 TCU is an excellent choice in a 10" tube. Don't overlook the 30 Herret - it was developed specifically for 10" TCs. You can buy preformed brass from EA Brown about as cheap as 30-30 brass.
Another option is Mike Bellm's 30 Bellm. It is a 444 Marlin case necked to 30 cal and shorten to an case length to meet Illinois' stupid restrictions for the deer handgun season. Mike says it is a legitmate 200 yard round.
Good luck!
