00,
I'm not a Harrier bubba but the F-35B brings far better avionics/sensor suite/situational awareness to the CAS arena.
I don't know if the engine change interval on your side of the pond is much different than ours but is they are similar than the F-35B "SHOULD" require far less maint. Thus allowing more station time for logistical chain support required; i.e. fewer wrench turners, fewer flights to get new engines in theater, etc.
The supersonic sprint can help. Over Anbar starting in 04 the USAF was supposed to provide all FW tanking; only problem was they wanted larger single gives further away from where the TacAir was needed in order to minimize their support required. The time off station was unacceptable so we had to generate extra sorties to cover the gaps and use our KC-130s for standby tanking in addition to other duties. A higher transit speed should increase the radii of acceptable coverage.
S/F, FOG