Good advice so far, I've not fished the Rio 40+ but use the SA Streamer Express Intermediate tip regularly. The Streamer Express is what is known as an "integrated head" (as is the 40+), that is, essentially a one-piece shooting-head-with-running-line-attached. These lines are designed to cast long distances using the double-haul technique; very handy for saltwater fishing where the fish seem so often to be just beyond comfortable casting distance.

Fishing a popper with an intermediate line sort of undermines the rationale of fishing a popper, since the line would pull the popper under and the primary appeal of the popper seems to be the v-wake disturbance it creates on the surface.

The Rio Outbound would is my choice for a floating line and is what I normally use when fishing the popper. Many sunk flies, particularly weighted ones, can be fished effectively with a floating line, it's rarely necessary to get very deep when fishing for coho or cutthroat.