I think there are two separate issues. If you are flying an aircraft which is only just adequate for a given field (I too think this has little to do with age) then you are taking a bigger risk then an aircraft which can get to 1000 ft by the end of the runway. That risk is made up of several elements;
A problem costing you 10% power on takeoff will put you through the hedge; the other guy will only be at 600ft.
The length of time you are too low to manoeuvre will be much shorter for the high performance machine.
I sudden change in weather (sudden 5kn tail wind etc) will put you through the hedge, other guy probably will not notice.
Secondly, a fully loaded 150 will be low, slow and have a much bigger noise footprint than an AT3 which has several times the R of C. The 150 will also be much closer to any nearby housing and make the locals feel less safe.
On glide ratio, my VLA is 13.8 : 1 if that helps, R of C at MAUW is 1700fpm and she is airborne in around 170m so 600m gives plenty of margin if something goes wrong. What are the numbers for a 150?
Rod1