I bought my set of 36mm carbs from Torquejunky and he told me that he tried them with cut springs and stock springs...he said it ran best on his quad with stock springs. That is the only reason I still use the stock springs on my 36s. I haven't tried the cut springs to see if how they act on my quad.
As far as polishing the slides, I don't see how that would hurt anything if your carbs are aluminum/metal. On my 36s, the slides are black plastic and so I don't think they can be polished.