I replaced the aluminum tank with the stock plastic tank, and it seems to be cooler. I will know next week. I might have time to install a cooler inline with the power steering hoses before I go to the track.
I finally found the solution for my powersteering issues, the electric pump I tried would not hold up either and brakes and steering fail.
What works perfectly is a Turn One GM style pump with external cooler and BMW fluid tank mounted right above the pump. Was able to do lap after lap without any problems.
I know this thread is a bit old but figured it is worth updating.