Take the whole lot off if its just for the summer, around 20% fuel saving, possibly 25% at a squeeze on proper road driving at the 55mph.
Considering the rapid rise in fuel costs, around 28p per litre since I bought the FL, I'd say its worthwhile.
If you are travelling the length of the country to an off-road venue, then remove the rear half of the prop and throw it in the boot, then refit when you arrive and go 4wd again.