Heres a thought, most bikes can run singlespeed without the hassle of a tensioner, bb30 and PF30 are covererd by beer components with their eccentric bottom bracket, as long the circlips are removable on your bb30 shell. With a standard threaded one there is an option of an exzentriker from trick components. So if you are happy with your Giant XTC why not buy a spare, rip the gears off, change the bottom bracket and bingo.
Had a cannondale the eccentric bottom bracket was a nightmare, currently run a Pace RC129 with slider dropouts and a Niner with a problem solvers E46 (which has a PF30 shell), so far very good.