You can catch 'em (and actually land 'em) on 6X. It all depends on your fly, and a drag-free drift. Your leader and 6X whippet has to land on the water with S-curves, and an upstream mend.
I don't like 7x whippets. Hook a big 'un, and you might not get him in.
Just my .02 cent's worth.....
So -- you were also in the big AZZ thunderstorm Thursday afternoon? It was a doozy. I'm still sore all over, and my hair is singed.