I do not agree that you should make your bp thinner, silver has superior thermal conductivity and thus you can have a thicker baseplate than lets say a copper one. A thicker baseplate means that the heat will be distributed over a larger surface area, though at some point it will begin to insulate the heat rather than cool it. The optimal baseplate thickness depends on the design of the block ofcourse and the material used, since your design does not rely on some advanced jet impingement technique and it hasn't got a central placed inlet, the heat needs to be more evenly distributed across the baseplate, thus a thicker baseplate is prefered.
Though i must agree that the bp you are currently using is kinda thin overall, the shallow channels you have will make the block quite restrictive, though if you have a crap flow in your system allready you won't notice any differance.
Please correct me if am totally wrong you thermal gurus.
Maybe silver = even more thinner bp? O_o?