There used to be a double reg option on the Daystate CRX and I think the Ar20 has something along those lines - possibly as that's supplied with the walther steel cylinder which is rated to 300 bar.

I've got 5 or 6 regulated PCPs. All have single regs and are very consistent. All are .177 and set at just over 11 ft lb except for a 10m FWB. All of these guns are boring on a chrono, any possible improvement would be related to gun fit or perhaps the barrel in one case.