I asked to reopen this thread to clear up a misunderstanding about pressure. My information was also incorrect on cart pressure being at 30 psi. It is more like 0.6 in3 of gas at 700 psi.
The whippet is designed to operate at 30 psi and is all over at least the US dispensing whipped cream. As an ASME Section VIII pressure vessel, it must be capable of 3x its maximum operating pressure, or 90 psi to be rated at 30 psi. That doesn’t mean it can be operated at 90 psi, for that it would have to be capable of 270 psi.
My 1 pint Whippet holds four cups of water, so when full at one pint, it has room for another pint or about 48.125 in3 head space. One 8 gram N20 cartridge raises that head space pressure approximately 14.5 psi, so it takes one 16 gram cart, or two 8 gram carts to reach 30 psi and three would put it at about 45 psi.
My Whippet is robust and will clearly hold 45 psi, though I don’t recommend operating one above its design pressure of 30 psi.
More to the question, as I stated previously, 30 psi pressure is not going to have significant effect on the EtOH extraction, if there is any benefit, it would ostensibly lie with any catalyzing action from the nitrous oxide, because after purging it is gone.
That leaves the issue about using extra carts to achieve higher pressures moot.