I always fill up on 93 even though I know with a stock tune 87 will be ok. One thing I always worry about is shady gas stations putting 87 in all the pumps. Numerous places in around me have been busted and they aren't all mom/pop stations either. Make sure to use a station you trust.
With my Cobra tuned for 93 I ALWAYS saved my receipts at gas stations when I filled it up. Not sure what I could do if I blew my motor due to 87 in there but its a start if you have a record.
2000 Mustang GT Steeda #0048 34k miles. 99 Cobra 4V swapped, FTBR IRS swapped, exhaust, tuned by James Gordon.
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.