If you are wanting to do the LMS route properly, you will need to have the car at their shop, dyno'd, etc so they can dial it in for you. That's their SOP, and it works. One of the things they have emphasized time & time again is that PSI is not how they make the numbers/timeslips they do.
If you want to be remote, datalog, and have the tune tweaked, then you will need an SCT tuning device and tuners like Unleashed or LET who have experience with the 3.5EB platform. Not to diminish LET in any way, but I know Torrie @ Unleashed is very good with remote tuning, has worked on many platforms from the mundane to the exotic, and so I'd stick with him if you switch to the SCT side of the tracks.
Maybe you can work with ajpturbo to see what can be done. He is in the process of self-tuning his SHO, and says he runs 22-24 psi (?) regularly no problems.
ARP head bolts are a great idea regardless. PPE & LME downpipes are among the best units you will find out there, both use the Magnaflow hiflow cats (if going catted). Unleashed offers a 3" downpipe setup that also works. No dyno on that one tho I believe.
With bigger or upgraded turbos, shouldn't really have to turn up the PSI as much. I believe we are looking at a practical street/DD limit of about 500 AWHP, and a strip-only limit of 600 AWHP. There are rumors that 600 AWHP is streetable, but due to the extremely limited sample, hard to speak for longevity.
Just some thoughts.
