I've been riding bmx for years, but it was getting painful and I wanted a fun alternative, so I turned to fixed. I received my new Windsor Hour in the mail a week ago, and I'm not sure if I got the right size. I'm 5'11'' but I have very long arms/torso and short legs so I chose the 54cm. People keep saying a properly sized bike should allow for a fist length of seatpost, but then I it seems harder to pedal/mount and I have a terrible pain in my butt(the low quality seat doesn't help), but my arms feel comfortable. When I lower the seat post my pedaling is more natural but my arms don't seem to be anymore. Is there any way to resolve this or is the geometry of the frame just not for me? Can this be me used to a tiny 20'' bike and I just need to adapt to the new style of bike?