Mike I've got a 65 gal Femco boom sprayer with a 3PH & runs off my PTO. Most of the products that I've used state how much of the product per 1000 ft or how much per acre. I don't think it matters how you get it on there whether you use 1 gal or 100 gal, just don't apply more than the label calls for for the specified area.
When I got my sprayer, I filled it with plain water & made several dry run applications paying attention to my ground speed & tank pressure. I just about have it down to a science now. Another thing that might help is using a spray marker. I don't use it much in the boom sprayer anymore as I have a good feel now as to how my coverage is. Helps quite a bit if you're spot spraying. Scott