"I'd say anything with 9.5 compression and higher really need the extra octaine.. "
Depends on the engine, too. The LT1 in my Buick runs beautifully on 87 at a 10.5 ratio. The Cadillac I owned before the Buick had some 273 cid engine and it would suffer detonation if I tried to run it on regular. It used a 9.5 compression ratio.
J_A_ B