Finally found Joe Johnson's old post on this subject:
http://www.chiefdelphi.com/forums/sh...74&postcount=9
He goes through the calculations for that particular gear, which happens to be rather similar to the size and load of the last CIM gear in the train above. The above gear has slightly more load and a slightly larger width, so it actually works out to about the same 11,000 psi stress that JJ calculates there, assuming 3x CIM stall torque. Even at 6x the stall torque, that'd only give you 22,000 psi stress, so you should be well within the tensile and fatigue strength of 4140 steel.
Joe's calculation only suggests that you're not likely to break off a tooth if you have your all those gears properly aligned. It's still possible that you'll wear it out rather faster than you'd really like.