i agree with everyone. the power loss thing is negligible, as said by Michael (it is there, but on a street driven car (read: not a track queen), you wont feel it, and would only see it while racing in conditions like Michael mentioned.
also, with a blower, i would not even worry about it. the blower makes it a moot point when talkin about power loss. people who told you about the power loss are theoretically correct, but practically speaking for a blown street car, you wont notice. i would prefer better protection at higher temps.
M1 tends to be thinner than a same viscosity dino oil. if you notice it taking a while to build up pressure when started in the morning, then do something. that weight of M1 has pretty good pour points and cold flow ratings.
also, synthetics clean things up, not gum them up (unless they were referring to the by-product of the detergents - removing crud and sludge). if so, i would have worded it differently.
good luck.