I think I posted the dyno stuff in here?! Its a really old thread.
I think you actually lose a bit of low end grunt when opening up an exhaust but gain in the higher rpm. I had plans to close them at the line and then have them auto open at just the right rpm, but I never got around to it.
The JEGS valves did eventually fail too (lasted 2x longer than race ready), but JEGS did replace them for free - its nice to deal with a company that stands behind their products.
The exhaust is still going strong and I LOVE it. Its the best mod I've done to a car, ever.