I hear that someone is working on a new 12 port head for these. I'm sure they will be out of reach for all but the most wealthy of sixaholics
You can get a thousand horses out of them if you have the money, but only for about 8 or 10 seconds.
The one I'm building should be pretty strong, but it's taking mucho dinereo. I'm still about 800 bucks from seeing it run. (with any luck at all)