have some fears on some mods- need support

hello all… well, I’ve been bitten by the damn EVANIX bug. don’t see how I’ll recover. symptoms are an insatiable need to shoot, and to tinker, and to see what an Evanix Windy City can really do, with some work. In addition to tuning, I’d like to get a bigger tank. the stock one is 400cc. I’ve found out that a Airforce tank and a 500cc Rapid tank is the same O.D. as the 400cc. Either tank will get me 90-100cc’s more air, depending on which I go with. would the larger tank, plus some tuning help flatten out the “curve” a bit? I’m also doing a .25 single shot conversion. My barrel choices are BSA, and of course Lothar Walther. Which should I go with? I don’t want it too long, so I’m only going with a 20″ barrel. that’s already 3″ longer than stock. Haven’t decided on a longer factory type shroud, or go with a HUGE 1.25″ one from Swift (if he’ll even make one for me). I’ve been going back and forth with this. here are my goals: have a fun gun, to mostly shoot long range, 40+ fpe. something I could run unlimited benchrest with, but not too seriously, just for fun, as I’m not planning on putting a Reg on it. I also want it very backyard friendly, hence the wish to go with a Swift shroud. Thoughts?? the rifle’s currently sweating it out back home, waiting for me to return to the States… It knows it’s going under the knife as soon as I get back. I’d like a bit of guidance on this one. some other small details: I’m going to change out the “gas block” (where the tank threads into) so that I can mount a better gauge on the left side of the rifle, and change out the stock fill fitting w/a foster nipple. I’m not trying to get MAX fpe with this rifle. I just want something thing fun that only shoots as hard as an M-rod… around 40+ fpe. thanks in advance!