Hmm. I countersunk all my windows 8/32 in the rear clam, doors and windshield. I've not seen a single crack in any of them in 14k miles. I think the trick is Fran recommended using black nylon screws. A huge amount of give. My last track event we ran counterclockwise on Eagles Canyon. The front was getting airbourne on bad pavement in turn 8 for four sessions x 8-10 laps. Still no cracks... no yellowing either since 2009.
The Nylon will creep and relieve some of the hoop stress . A stainless fastener will not. The difference between an acceptable level of stress and too much stress could be a little as a quarter turn of the bolt. It is very difficult to control torque on small diameter bolts. Polycarbonate is much stronger in compression. The following is from page 20 in the "Lexan Sheet Processing Guide" attached.
• Do not use countersunk head screws as the ‘wedging’
action of the countersunk head causes excessive
hoop stress on the sheet. This can lead to part failure.
• Be sure that all oil, grease and other coatings are
removed from the screws before assembly. Certain
oils and greases can cause environmental stress
cracking.