I was actually down at Bullet last week asking a few questions about their HTV1900 kit as I will hopefully be purchasing this setup to use on my 1UZ Hilux sometime very soon.
Anyways, the guy I deal with their was saying they done some back to back testing on a Chrysler 6.1L Hemi. They compared one of the HTV blowers (not sure which size) against a Whipple twin screw of the same capacity, running the same boost pressure, just a straight swap over, nothing else changed, and he said the HTV outflowed the Whipple and made another 40hp.
It is a great step forward in the innovations of the roots type chargers that's for sure, real competition for the twin screws.