I have used my Conquest with a Gas-Thru on my EvoX for a couple of months.
Several times I was well below 1k psi when I came off the field and the chrono did not show increase in velocity.
Spike... no. If I got closer to 320psi left then I would expect some change in performance but who carries that much paint? Shooting 4000psi+/- from a 68ci tank on a cocker is A LOT of paint.
All-in-all, I'm happy to put a Gladiator inline to insure the very best performance.