Oh dear .. appears I have been a tad lax again with my words. Perhaps I should have said something like .. one can use the SID OEI but it is no different to working out your own escape .. you still have to get all the relevant obstacle data and do all the sums and work out the limiting case for the takeoff to determine the relevant RTOW. The only advantage of the SID is that it fits in with ATC ... if may very well not give you anything like an acceptable commercial RTOW...