Depends on the performance you want, and how heavy you build.

A 70 will give good performance, but I personally would go for the Saito 91 for real "unlimited vertical". Remember that a Saito 91 weighs less than an OS 70, and not much more than the Saito 72, so weight is not an issue here. YS 63 would also work well as blvdbuzzard said.

Sprink