Phil, is this for primarily personal use, or to record various and sundry vocalists?
Don't (yet) own a 610, but even the stock tube wowed me when trying SM57>610.
But the Shure Unidyne III coloration + 610 coloration/thickness works A-1 on me.
YMMV. At least as well as SM7>Avalon 737, for example.
Chris