would the 1000' minimum equally apply to slower planes and to the faster?
Jan, just like Mark1234 mentioned a few posts back, there's no hard and fast rule about this. Sure, you can probably accomplish a 180 degree turnback in 1000' even if you're not applying perfect technique (as long as you bank sufficiently - there is no room for a rate-1 turn or something similar).
But the emergency is not over once you've made the turn. You were climbing out at some angle at Vy from the threshold, now you're still as far away from the threshold as you were when you started the turn, but you lost a few hundred feet and you have no engine power. Is your glide angle sufficient to reach the threshold?
I have seen a Pitts Special climbing away after departure at an angle of 45 degrees. Now the Pitts is reputedly not a good glider, but it should be able to glide at significantly less than 45 degrees nose down. On the other hand, our DA40 with the 135 HP Thielert was normally just able to clear the trees at the far end of a (long) runway, if fully loaded, and would never be able to glide back to the field after a straight out departure. Even if you climbed to 10.000' and then turned, you would not be able to make the runway. (Despite the sailplane heritage, the DA40 still only has a glide angle of 1 in 8, and that's about equal to its climb angle.)
And another factor is how much runway you still have available ahead of you, when you rotate during the take-off. If that is significant then that bit of runway may still be reachable from the glide, whereas your original rotation point may not be reachable.
(And to put a bit of perspective to the debate, and how dependent it is on airplane capabilities and circumstances: In gliding we fly a full (although tight) circuit when the winch cable breaks at 300' or above. Yes, you read that correctly. A full circuit, with four 90 degree turns, to a normal landing in the normal landing area next to the take-off area, from 300 feet. But a winch launch cable break happens by definition *above* the airfield, not beyond the threshold, and any reasonably modern glider will easily beat a 1:30 glide angle.)