I think there should be an additional setting, "Risky, may never confirm". Since four choices are too many, I think the lowest-fee setting should be repurposed for "Risky".

But actually I think an even better solution would be to show the confirmation time ranges or at least confirmation time averages that a certain fee would have achieved during the last 7 days, along with a warning that the future is unpredictable. That could be a slider with markings for satoshi/byte. The slider could have a red, a yellow, and a green range for risky, slow, and fast settings.

Your customers are your best designers. (:-)