OP - welcome back! I was just talking to someone who went from M3->GTR->M3...had similar impression on GTR. I was surprised to hear how much maintenance was...I thought since it was a Nissan that it would be relatively inexpensive...guess that was a false assumption on my part.
I'm impressed to see your FR-S have such a good lap time...I thought surely a stock M3 would still have a better time but like you said - on a technical course, if the M can't stretch it's legs, then the power differential is somewhat negated.
[08 e90 M3. Jet Black/Black. Dinan Rear Exhaust. ACM Test Pipes. ESS Tune. Eibach Pro-Kit + e36 bumpstops. 18x10 Apex Arc-8. AA Air Filter. RPI Scoops. CREE Angel Eyes. OEM Blacklines. Black Reflectors. Gloss Black Grills. Matte Black Gills. ZCP Shift Knob]