My opinion:
Use a tranny that is reliable and consistent. You're talking about racing, not just having fun. I know at your level this may sound crazy, because you have certainly raised the bar, but it's still simpler and better to increase hp or reduce weight, rather than monkey-ing around with fancy, and more complex (broken), transmissions. You have so much power to weight that, in my mind, mechanical efficiency is not the prime consideration. Putting the power to the ground consistently is. If mph at the traps were the issue, then I might say something different.
If you can get a lock-up convertor to work, great. If not, focus on hp and weight, or a different conventional torque converter.
JMO,
pauiie