Don't know what Caddy recomends for fuel, but one thing for certain the caddy's 10:1 compression won't handle near as much timing advance on 87 octane (all other conditions being equal) as what 9.4:1 will. The quickest way to make a engine lose torque under acceleration is to have the computer start retarding the timing a little because the knock sensors sensed detonation occuring.
I would rather have 9.4:1 on 87octane with more timing than 10:1 on 87 with less advance. Now higher octane would be a different story alltogather, but you still might not break even considering the price difference for premium fuel.
Don
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