My first cub had square tips, Hendrickson (sp?) I think. It stalled with a dramatic break, and you could not fly it down close to stall on approach, because if you did and it stalled, you were a statistic.
My current plane with round tips has a slight burble at stall, so I can fly it right down to the burble and add 25 rpms and continue, no nose down break, so it is not the risk of life and limb...
The square wings with more area gave more lift, but the round tips allowed me to use the lift I had to a better advantage, and once down I can kill my lift and get on my breaks better for a shorter stop... I actually fly this plane slower on approach...
That said, I do have vg's and thrustline on this bird now. It is set up the way I want it, and I like it. I never got to fly a plane with, then without tips to check, but my friends did some testing, including putting one Madras tip up, and the other side down, and could not detect a single change.
Were I building a plane to win Valdez, and nothing else, I might have the tips on, or put a big piece of plate out there sticking up 2" and down six inches to stop the flow around the tip...
for practical use, I would bet that most of us could not measure the difference in performance between the droop tips and other square wing tips.
But round wings shed brush better!
And they look a whole lot better to purists
(back to my hole)