Hi Daniel
That seems like a pretty good setup, it is basically the setup we used on the S4 all last year and was developed on a bumpy astro track and a multisurface astro track over the winter of 06/07.
I would add an internal spring to the front shocks (the ones that you get in a XX4 WE) it makes an AMAZING amount of difference to the stability of the car "on power", it makes it possible to jump on the power where you were only able to feather the throttle in.
Something else we have found is that the B44 prefers a slightly more damped rear end, currently orange piston 30 weight oil, however, if the track is very bumpy and does not have any big jumps then blue piston 35 weight will be better.
Also try long wheelbase if you are on a bumpy track, we have found this to make a big improvement.
I also prefer a red front piston which I find gives the car a little more supple feel as well as a touch more steering.
I have considered 5 cells and a 4.5R but not tried it yet, you might want to consider a smaller rotor in your 5.5 with 6 cells. Might calm down the power a tad, the shaft drive is very responsive when you get it wound up.
Hope that helps
