to answer your questions more directly ... the 87 would most likely have the higher EGT's ... from my experiences ...
I was on another forum and the subject came up. From my experiences with diferent stock and high performance engines I noticed lower EGT's with higher octane fuel also. Apparently this other guy is some chemical engineer and swore to me that higher octane burns hotter. I was trying to explain to him that what happens when you run low octane in a high performance environment. I've seen higher EGT's with 91 then I did with race gas in the same exact motor. Without any change of the blower pullies of course. :rollside: