I have been running my MSM turbo (on 96 8.7:1 compression block) for almost 6 months at 14-15 psi peak boost tapering to 13 at redline. 238hp/232tq. I would not feel comfortable pushing my stock rods or 5-speed past this point. No issues on the street, but I still have to wait for my first turbo'ed track day later in the year to see how it holds up on track. I am running sequential fuel and spark on MS2e with GT500 injectors, so my fueling is much better than any factory ECU setup.
I have been keeping an eye on MAT with different boost levels and saw only minor changes between keeping the peak boost at 13 vs 15. It did become inefficient when pushed as high as 17 and I even saw reduced hp/tq on virtual dyno. There is no HP benefit going above 15.
I have noticed that on extremely long 5th gear pulls at high >5000rpm that MATs will creep up 20-30 degrees more than the usual 30-35 degrees for a normal 2-4th and halfway through 5th pull. The little turbo does heat up on extended 5th gear runs, but I don't think it is much better when peak boost is kept below 13-14psi. I need to do a run with boost limited to 13 psi and see what the MAT impacts are. I also need to do some IR thermometer readings of turbine housing temps after a 13psi peak pull and a 15 psi peak pull.
I was considering only running 13 psi for my track sessions to be safe. But have not found a significant difference in temperature indications between 13 and 15 psi peak boost.
With the research I have done I did not find any manifold cracking issues related to too much boost. At least not unless a fastner or some other component failed first.
I will say that this thing falls on its face after 5500 rpm. Boost comes on nice and early and hold strong through midrange so it is nice for the street. I am concerned that I will be running out of steam in the higher RPM range for most of my driving on CMP. Hopefully I will be able to shift to the next gear and keep RPMs lower in midrange instead of reving the crap out of it and hanging out near redline a lot like I used to do n/a.
Everyone that I have met that uses a MSM for serious track use, not just occasional track days, ended up going to a different turbo that could breathe better and more efficiently in the higher RPM range. I only do one track day a year, two at best so I am hoping the factory MSM will meet my needs for now.