Hi I use a 10/22 clone with a Shilen select match barrel (16.5" long with a muzzle can suppressor) and topped off with a 4.5-14x50 Leupold with a mil-dot reticle. I sight it in at 70m with Winchester subsonic and 5mils gets me out to 150m (I have a trajectory table taped to my stock) over the last summer I would have had 70+ 1 shot kills at 150m sometimes in winds requiring upto 3 mils of hold off. My furthest confirmed kill with Win subsonic is 220m.
Another option for a challenge is a LD CO2 pistol from www.mac1airguns.com
it is about 10ftlb's at the muzzle with 22 pellets and I have shot 50 plus rabbits at 20-33m with it my current record with it is a magpie with one shot at 49m. It is very accurate less than 20mm at 30m (3/4"at 35yds) the shooter is the limiting factor at the moment.
In the August 2004 Vol. 7 No.11 Small Arms Review there is a article on Mark Whites suppressed Rugers see www.soundtechsilencers.com
his premier pistol is the integrally suppressed Ruger KMK-512 which drops the bark dowm from 152-154dB to 112-116dB (action noise is 109dB and a CO2 air pistol is significantly louder than a 112dB).