While I normally shoot the standard loads, I have shot a number of MBs in my SX3. Mine is the 3" model with a 28" barrel. I've had good patterns with a number of chokes. The SSX has put up some very impressive patterns that are dense and even. The Wright's have also done very well. It turns out that many different designs/brands of chokes can throw very good patterns. That means that a .643 can do well in one brand while a .670 may do well in another brand.
Thanks,
Clark