I had a different issue with the 324's. When I used 324's my shins were always beat up. The pedals just has a lot of sharp edges, that seemed to target my shins. Even though I am using 520's now, I still have my 324's "just in case". They do have some advantages. My wife swears by them, but they don't seem to eat up her shins.

My shins usually looked like this for the 2-3 years I used the 324's


Shimano 324