Okay, I think I'm starting to get a pretty good handle on fast thirds finally (at least in right hand for now, somewhat in left hand too), but what about sixths? When I improvise, I typically make my thumb jump around a lot while the rest of the fingers play the scale on top. I've checked some technique books for some ideas, and they seem to be pretty similar except the bottom note goes 1 2 1 2 1 2 etc. I find this scheme exceedingly awkward*, especially when improvising (my hands are not exactly big, the biggest interval I can hit with ease is a minor tenth on the black keys). When using sixths I am typically not trying to dazzle anyway, but say some poignant moment came when I DID want a dazzling speedy run of sixths....any advice?

*in other words, I feel like my hand is twisting really far to the left, and then to the right, to accommodate the suggestion of this technique book. I'm beginning to wonder if technique books are always written by people with massive liszt like hands. this also makes me wonder if such techniques, practiced too much, are what busted Schumann's hand and also Scriabin's.