Ideally you want about double going in, as you have after the Vert Reg...Tommy's gat will be running as low preassure as possible, as it makes cocking easier, therfore means cocking preassure can be lower..all make sthe gat faster (not too low tho!)
450 Psi may mean the gat farts at high ROF's, or you may get drop off, because it doesnt have time to fully recharge between shots..so ideally yes, 550 to 600 psi will be good...if you are changing from a bulky Adj system to a preset, which is what I did (sort of) I would recommend a Nitroduck Extreme reg, which looks lieka preset, is very similar in length, but is infact adjustable...also, I have found it to be more consistent than my MaxFlow that I had...+/- 1-2 Fps over the chrono..which all add's up to improved accuracy.