Sounds fun. And scary. Breaking traction at high speed is very unnerving but entertaining at the same time, and that's what you have to watch for, the fun can turn dangerous quick! Seems like everytime I take my car out I find myself purposely spinning the tires from 60-80 just because it's so much fun; I don't even bother with spinning them from a standing start or anything slower than 50 or so because it's boring.
Since I finally got my injectors swapped, I can wind the thing out now-- I had something very similar to your incident happen yesterday afternoon, the car got loose at about 100 in 3rd gear. I put my foot in it, it hooked for a moment then it did little side squirm, so I countersteered and kept my foot in it because it felt like it hooked back up. Just when I thought everything was OK it squirmed again, then it went into side to side wag just as you experienced. I gathered it up, slowed down, and then I started thinking about what could have happened and that's when my hands started shaking a bit. Moral of the story: don't think. Had something happened though it would have just been between me and the walnut orchard, which would NOT have been pretty. Trees don't move much.
I had another high speed incident last year with my first hydroboost experience-- I twitched on the brake pedal slowing down from the top of 4th gear and locked up all four tires and pitched the car sideways... at just over 150 mph. By the time I gathered it back up the speedo was reading 110. I had to pull over, get out of the car and take a breather after that one. You should never, EVER be looking at a concrete K-rail at 150 straight out of the front windshield.
Remember, keep the shiny side up!
On a more technical note, have you ever tossed a TC into your manifold? I'm very interested what your discharge air temps are like at 10psi without an interooler.
Troy