I've never done it, but I've seen it in action, and the 10's are impressive. Like Swamp said, a 10 will out-pattern a 12 all day long.

I've patterned a lot of 12 guages for turkey hunting and turkey shoots, from 2 3/4 to 3 1/2" and I've never seen patterns from a 12 that even come close to a 10.