I'm looking into using either my Amex or the Visa for a personal car rental of 11 days. Since I'm looking to avoid possible risk of dealing with any accident through my primary insurance company, and I don't want to pay CDW...

I can't find any info on this online. Amex appears to offer a $20 primary coverage, which works for me, but if MR Visa also has such an option, I'd be interested to hear it.