Thanks Scottie it has stayed together fine running at 17psi now.
I've upped the boost again and it has run great through fall and winter. I made a larger 3.25" downpipe that I just put on and have a larger meth nozzle. I also had the driveshaft rebuilt (again), new uuc trans mounts, guibo, and whiteline front swaybar. I will be tuning up to *cough* 20psi and dynoing again by the end of this summer as to enjoy the car before testing the limits. BTW this is a 9:1 compression b35 with only a slightly thicker mls gasket and stock bottom end with 270k. The way I see it as long as the IAT is reasonable (below 100F) this can be achieved with water/meth injection and the upgraded k27 should still be making power. I am now at the limit of the 745i stuff. Hoping to make 400rwhp and 500rwt. Once I do that I will be selling this setup and tune and upgrading to a much larger turbo and manifold.
On a mustang dyno this morning I made 384 hp and 493 tq at the wheels! I will post some pics later. This was 19psi peak tapering to 17. 20psi and I will have surpassed the goal. I'm currently waiting on a new meth filter bowl which broke after the first run and started leaking.