I tentatively suggest the XP ranger .45 with 36" barrel. Can make 900 FPE according to mr hollowpoint. As others noted, not particularly practical without a booster pump as it fills to high pressure. Also this gun is absurdly long. They have other absurd calibers like .58, .72 and .82. Oddly, no .50 cal
Still, I'm considering selling my bushbuck and getting a 36" barrel .45 XP airgun. XP airguns is coming out with a bullpup version soon, so it wont be quite so absurdly long. I thought the bushbuck was long, but the ranger is even longer, so I do think the bullpup will be preferable to me.
Gotta get a booster pump first, will make life much better. Even my .22 huben goes through air quickly. The bushbuck gets max power at 3800 which is bad enough without a booster pump. Although 3800 is enough to use my other airguns for a while. Just have to shoot the bushbuck first when I go to the range. To be fair, the bushbuck can be filled to just 3000 psi to shoot smaller slugs on low power
No way would I get any airgun that needs more pressure than the bushbuck, and even it's 3800 is steep. Unless one of the following applies
1. You have like 5 large carbon fiber tanks cascaded.
2. You REALLY REALLY enjoy hand pumping. As in, you like pumping more than you like shooting, where shooting the gun is just the means by which you get back to pumping.
3. You have a booster pump setup
4. You have one of those mobile compressors that can run off of your car's battery etc. and dont mind waiting the 5 or so min it will take to fill your gun, potentially for EVERY shot. might not be the worst thing if it has an auto shutoff and you have other stuff to play with in the interm