I flipped a lot of tubes in my Dual, including the KT's (my friends and I were doing some rolling when I fist got my amp) and for what it's worth, the best all around tube for the Recto is the TAD 6L6GC. I also like EL34's, but I loose whats left of the clean channel, same with the KT88's, the KT66 sounded a little harsh on channel 3 Modern, and the setup is you mentioned is way expensive to experiment with.
Just my .02