Length and critical speed are bigger considerations than power level (believe it or not). I know alot of guys running mild steel shafts in 950+ hp cars....because they are short and critical speed is acceptable. I had to go to a 4" aluminum shaft because my 8100 trap RPM and 49" long shaft. Mine is from Inland Empire and I got it at a great price thru John Holt race cars. About any of the reputable places will build you what you need in the correct material.