Your 100% correct, almost all info out right now for this platform is speculation when it comes to specific details. It's standard tuning practice that as manifold pressure increases, timing decreases. Typically till you hit the engines VE at which point you can level it off. But how much is left to be unknown at this point. But considering this car only runs 15ish psi factory and we are talking timing levels that are 5+psi above factory levels I would figure it's "safe" to say at that high a level Mercedes slams the timing to the basement to protect there motor. I wish I had AEM installed on this computer so I could make a quick timing table and post it to give an idea... but anyway in words I would venture to say beyond the factory boost levels the timing slowly tailors off, maybe 1-2 degrees per psi, but at some point before there factory map ends I'm sure they plunge it (drop 2-4 degrees). And for all we know that point could be right there between a 181 and 185's boost levels. Who knows...

Temps kill timing. On factory cars a huge portion of that has to do with emissions. If I recall someone, probably woody posted 92 degrees or so was the Magic IAT that the car started yanking timing back.

Good news is IAT's are simple to control, as you posted along with ECT's Add to that simple Water/meth injection kits, or heck even a super, super, super small wet/dry shot.