I WAS using 91 octane in my Taurus because my Chinese engine opted for it. When I stopped using the Chinese jobby I went to 87 octane and noticed 0 difference, actually if anything it seems to run better on the lower octane - but I can't really tell.

I wanted to use Pennzoil Air cooled oil for break in but had to buy 12 pints of the stuff. I'm still using it at 50:1 10 or so gallons later and plan on doing so until it's all gone.