I went from a stock PA-11 tail (unbalanced elevator) to a PA-18 stab/elevator when I installed flaps. It's heavier but I felt mo better for control especially when slow -
Sometimes it's good to step back and fly the stock plane enough to note any changes mods later make. As built Cubs are a fine airplane...not sure of the exact % but surely 3/4 or more as good as one later tricked out. Empty weight is very important and the first PA-18-150 was a fatty at upper-1100+ (I'm being gracious-she was a lady). It flew well but the weight could be felt especially the extended wings. The PA-18A-150 above was mid-1000 when done and I liked that feel. So maybe do a few improvements to keep the air under the wing and on top of the tail plus good rudder and keep it light as possible.