My personal best growing up was a 35lb. beast I caught right under a small waterfall on a creek back in Iowa growing up. We used to catch a lot of spiney softhshells also, with females being close to 18" across and somewhere probably 6-10lbs. I don't target turtles anymore, unless just for fun to show a big snapper to my kids, but we used to do a number to them back in the day.
My second wife got a 25 pounder in a gravel pit near Correctionville Iowa back in 1991 we weighed it at Fisherman's Haven in Sioux City then had a fish fry and ate him. We learned that turtle ain't good fried fresh it has to be cooked slower.