by your decision to try HFT rather than 'buy a dedicated FT outfit'. I've only been doing FT for about three years now, but I don't grasp the distinction - maybe you or someone else could educate me. I have two FT guns - an RWS 52 and an RWS/Hammerli 850 HPA. We shot an 'all HFT' match at IAFTC last fall, and all I did was replace the 6-24x scope on my 850 with a 3-12x. I won the match.
The main distinction I see, again - I hope someone will correct me if I'm wrong, between FT and HFT is the 12x scope limitation. That coupled with the fact that you might be using different shooting positions would lead me to posit that an 'ideal' HFT gun would be a PCP or HPA gun, shooting near 20 fpe - that would eliminate the hold sensitivity usually associated with springers and make the long distance ranging less critical. As mentioned, it would seem a Marauder would be a good choice as would my aforementioned 850 HPA (see the850store.com for more info).
I'd also suggest that if you already have an air rifle - simply take it and go shoot some FT matches. You'll be able to make a much better decision for yourself if you have the experience of a few matches under your belt - even if you were not 'competetive'.