I set up my new rain barrel. It is fed by the gutters on the north side of the house which have leaders on both ends. After less than an inch of rain I don’t know how much water was in it but it was much heavier. I’m now wondering if it would overflow during a heavy rainfall.

@paulc - yes it would.
I have a large 250 gallon heavy white HDPE recycled food-stuff container with one downspout feeding into the top of it, draining one 34' eaves trough on one side of my garage.

A good overnight rain fills it to overflowing by morning.