I have 572 hemi in a 4100 lb 67 gtx and was told by Keisler that their trans would likly not handle the torque it puts out, so in my case there is only one choice and am prepared to wait till Jamie gets it ready. I am confident that he will have a fantastic trans when it comes to market and really appreciate the fact he is making sure it is ready.
I currently have Keislers A41 4L60 automatic in my car and it has failed to handle the HP & Torque. I also really believe you get what you pay for.