As for the big US bank texting that silver would be worth 1/5th of gold, yeah, good luck with that. A twenty multiple doesn't even match with current metals trade.
But in the end, if we went to a metals backed US currency, we'd be much much worse off than we are today. We don't have the mining deposits available without years of reopening and starting up mines again, and it'd just be a constant downward spiral as we offer more and more greenbacks to purchase the metals we're going to back our currency with. The constant devaluation would just make international trade turn to another currency to do their trade in while we self destruct.
Feel free to hedge with metals - it just wouldn't work for backing our currency at this time.
It's the ratio that would matter then, not the nominal.