First, stick with what you state law allows. Superdex: Colorado law does not specify single file - rather it says riders traveling two-abreast shall not impede the flow of traffic and must stay in a single lane - Colorado Bike Law | Colorado Law.

Some pseudo-scientific studies suggest that it takes about 80 percent longer for a car to pass a single file group of cyclists vs. double file.

Studies on crash statistics show that solo riders are more likely to be hit than groups. The data is not clear on whether double file is safer than single file, though riding double file does increase the visibility of the group.

As for waving cars around, there are arguments for and against. FB pointed out the against arguments. And any riders pulling off should check that the road is clear before doing so.