I have done a lot of testing with GO over the years, using many different gloss papers, and different amounts of GO. I found that our standard 30k units of GO works well on a wide range of papers, but some work better with two coats (such as Canson Baryta Photographique), or one coat of a slightly higher limit. Yes, there is a visual difference of printing two coats of 20K vs one coat of 40K (I found one heavy coat can reduce the sharpness). If printing two coats of GO, dry the first with a hair dryer before printing the second coat. In my testing, two coats is all you need when working with papers that need more that one coat, and three coats can be too much (though, I didn't try different amounts or drying times, because I think two coats is the maximum needed).
Best regards and happy printing~ Dana