From what I've read, a 2x3 rectangular downspout is meant to drain 600 square feet of roof. But surely that depends on the rainfall intensity, doesn't it?
600 square feet of roof in Idaho is going to be a hell of a lot different than 600 square feet of roof in Hawaii.
I have 385 square feet of roof which will be handled by 25 linear feet of 5" K-style gutter, in an area that receives a maximum rainfall intensity of 6 inches / hour over a 5 minute period [chart]. Will a single 2x3 downspout be sufficient? If not, will I have to upgrade to 6" gutters in order to accommodate a larger 3x4 downspout, or will a 3x4 downspout still fit on a 5" K-style gutter?