Mutt,
Sorry if we are scaring you, I'm open to suggestions if you have any, what would you do?. I know exactly what I am going to do if an engine expires and we are both briefed on the plan of action before take-off. 12 miles is enough to reach 1500ft, after which you are on your own anyway so you have to have a plan for that bit. Obstacle turns on runways that need them tend to have taken you away from the high ground but some don't. I seem to remember Zurich was one place where you were not pointing in the correct direction.
BOAC.
I agree that Perf A (or JAR whatever) is just a grouping. It is a grouping whose take-off and climb performance is certified using a set of rules and parmeters that ensure that various safety margins are met, to meet those margins you must operate within the regs. The a/c manufactures do supply take-off performance software and that is what churns out the figures on the specific runways pages in the manuals. As you said Perf A does allow turns in the take-off flight path and these can be entered in the software for places that require obstacle clearance procedures. If the page makes no mention of a turn then these figures will be based on straight ahead not on the SID from the runways, at least in our company and I suspect most others, it's hard to imagine someone keeping all the hundreds of pages updated for SID changes etc.
My first post was a dry look at the regulations, of course normallly you are not at max. weight and not obstacle limited and turning into the SID may be quite safe. You must realise that however that it is very unlikley that the figures you used cover the path you are now following.
Most of the time you will also miss any obstacles by a lot more than 35ft, if you are obstacle limited at max. weight or at reduced thrust you won't have much more than that. You may have less if you have rotated too slowly or have a slight tail wind above the runway that you were unaware of.
As Safety-worker says, a very interesting thread, I hope I never have to put theory into practice.