Just a couple thoughts. As long as you get the hydraulics & pedal ratio correct, there isnt a problem with the small bores. I am guessing you are trying to stick with a tandem MC and that limits options for that item, when dealing with the SL6.
I hate to say it, but we live in a first-gen world. That said, I would venture to guess that Wilwood did not take into consideration the light (5.3:1) pedal ratio of the second gens (but the first gen has the near universal 6:1 from the factory). I have yet to see many 2Gs with the SL6 calipers and guess that Wilwood is listening to the 1G customers & ignoring/missing the pedal ratio disparity.
Shane
Unfortunately the tandems currently limit you to 7/8. It was either buying new bigger piston calipers or buying and fab'ing a dual MC set-up. I choose the duals. Going with the duals will give you more flexibility and the MC's are cheaper. Would work with the 5:1 pedal ratio