Hi,I live in Pittsburgh and my area is all hills and I need to climb them at more than 15 mph so I'm gonna change to 5.5g roller weights. My question is what size does my agility take? I've heard 16mm 13mm and dont want to order the wrong ones. And I would also like to know how much top speed will I lose, I now average 35-38 mph on a flat area but I'm willing to sacrifice a little to pull hills better. Thank you for your responses in advance Dale