But with alloy struts won't you just have the same problem as with the Bagman 2? AIUI a heavily loaded bag causes it to flex enough that the support struts fail through fatigue, while the steel Bagman frame is fine. OTOH alloy pannier racks seem to last ok, so IDK.
And then there are these struts that are made to be used with the basic bagman http://practicalcycles.com/products/365984--carradice-bagman-alloy-support-struts-converts-bagman-rack-for-heavy-loads.aspx