Here's a very simplistic take: I'll use Vy for 'normal' ops 'cos that's what the POH says for normal - it says Vx is for obstacle clearance. I don't personally think the difference between them is significant in terms of /EFATO (gut feel).
As for the turnback - (mostly) NO. Obviously it's very type dependant, your milage may vary. I've played with simulated EFATO & turn at height, and get a 350-400ft loss from a Vy climb for a 180, best technique seemed to be to roll to 45-60 degrees and pull into the stall warner, relaxing back pressure / allowing the nose to fall as necessary. That equates to roughly the same airspeed as level best glide. Pulling into buffet makes things a bit more interesting, and probably not clever close to the ground. Both require excessive back stick, indeed I managed to put the stick on the back stop before it actually began to flick out of the turn.
Disclaimer: This was done in an aerobatic category Robin that I spin regularly, at about 5000+agl, and I'm properly trained, current, and endorsed for aeros. Please don't go and spin something in doing the same.
Conclusion, under 500, I wouldn't even think it. Somewhat over 500, maybe, but it's very dependant on position/ other options; I fly from a large field with long parallel runways where 300ft over the fence is not uncommon and it's surrounded by housing estates. In any case, it won't be a return to the runway, it'll be a hard left/right for an open space - taxiway, grass, whatever.. Equally, the crossing runway may well be an option.
Last edited by Mark1234; 21st Apr 2009 at 04:02.