Hi Doz, Dean has covered it quite a bit.
Having done both HFT and FT ( i have a big Sightron ready to roll for the winter league) i would say that finding the right HFT scope is at least 10 times harder that finding a FT scope. Having the px and mag fixed causes all sorts of problems that only appear when shooting in a comp so a scope you think is great on the zero range may not be so good on a course. Shooting a scope with fixed px and mag can be tricky and although there are some nice scopes out there i still keep coming back to the 10x44 MTC Viper. Probably one the most popular HFT scopes but does not suit everyone.
Are you at Newbury for the next GP as i can ask if Trev Ryan can bring my spare 10x44 Viper down for you to try out for a few months.