The H on the new plastic is a different material than the old original plastic's. I recommend using the H labeled plastic's. The H plastic is not harder than the stock stuff, they are just more durable due to the different material. performance is better overall all also. More consistent and the rear end is more stable also.
Hope this helps,
Capricorn RC, Capricorn Tires, Novarossi World, Spektrum, Horizon Hobby, PROTOform, RCTarget, IGT8.