The biggest one I know of is the 46 liter 929 Bestem box. I have the 2012 42 liter and am very happy with it. Good quality and inexpensive. Bestem makes a Suzuki Burgman mount for it also. You can get the pair for under $200 delivered, an excellent value in comparison to Others.
If you do choose soft seat bags (which hold the load lower and are therefore less likely to unbalance the bike) the Ortleib Dry Bags are about the best you can get. They don't require any special mounting hardware either.
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