It's worthy of note that Piper says best angle of climb in the Cub (assuming a stock airplane, of course) is 45 mph and full flaps.
That's best angle, though.
Every airplane is different, and best rate is very different than best angle.
The Husky flaps are very effective lift devices, up to and including 30 degrees of flap. The factory recommends 30 degrees for takeoff, and I agree. These are Fowler flaps, though, as opposed to simple flaps on the Cub.
I know of at least one Husky that was modified to 40 flaps and the assessment of the owner was that it didn't change that much.
Every airplane is different, though, and on extended climbs (as in once you are past the trees, rocks, etc) I see no advantage to using them in any airplane I'm familiar with, unless you need a really steep angle for some reason.
It would be interesting to see what more flap does on a Cub. I'm not particularly enamored with extending the flaps into the fuselage, though it's not that ugly. I've seen video of the tail on one of these cubs with the tail tufted, and there was a lot of disturbance over the tail with flaps deployed. Not sure that bigger flaps won't do the same, but rigorous flight test would tell that tale.
MTV