I think the +4 gets the nod in the runtime department.
The OS Speed gets great mileage but its primary purpose seems to be to haul the mail not getting extended runtimes...it just happens to do both
The rest of the RC world was forced to start to focus on mileage by the V-Spec and Speed and in doing so I think they have eventually surpassed them. In talking to Ed Bridges (EB Mods) he said they do this by using a smaller crank opening which in turn gives less HP. This was during a conversation about why the GRP engines were capable of such impressive run times.