The stretched version tends to be a little more unstable in pitch although this is really is only noticeable when instrument flying. For lifting, I flew both short and stretched versions and there tends to be very little difference. I can't comment on operating in higher temps as we unfortunately didn't have this problem suffice it to say that no Bolkow has a great surplus of power! We use to lift up to about 450kg but you won't have much fuel in the main tank to do this - the low fuel light in the supply tank will become well used. We had floats on ours which will of course have reduced the payload a bit.
I loved the machine even though it did try to kill me on one occasion! Make sure the hydraulic change over is spot on.