Hartwell is more of a trophy lake. It's a low density, larger fish fishery. I think you were in the right areas. Anywhere above 85 is productive this time of year.
Look up the striper kings website, They fish out of hartwell.
Are you fishing the SBC in a couple weeks? Info is going to be pretty tight lipped until that's over.
I'd cut your losses and head down a lake to Thurmond/CH. you got big fish and also plenty of smaller fish and hybrids while you wait for that big bite.