hi, has anyone tried to change from a stock (shimano 105) compact 50-36, 170mm to a standard (shimano ultegra) compact 53-39, 172.5mm? what happened is, i found this Ultegra w/BB from competitive cyclist that they sold brand new for only $120 (this is the only size available), which i think they made a price mistake, last tuesday. it arrived thurs and had it installed friday. i know it was a good deal that i didnt want to pass on. i did a 40 mile ride today and had a bit of a hard time climbing the mountains. now my hips are aching a little. i am 5'6 with 29-inch inseam. is this crank ok for my height? if yes, do i just need to get used to a 53-39 from 50-36? need your opinions please....