There were 6.1 leaks a while back (and I do mean a while!). While I don't think anyone would recommend doing it, it is possible to load it onto a 9930.
There are no benefits of doing that, you would be running an early developer only build, I think even when the 9930 was first put on demo it was running an o's with 7.x only the very early ones still in Canada were 6.1
Originally it wasn't gonna bump to 7 as it wasn't that much of an increase but the new phones had such a leap in processing power they could do what RIM chose to call liquid graphics, and since java is getting ditched anyways they went ahead and bumped the first digit for marketing purposes.
But I digress, no good reason to downgrade your phone dude.