I would think Rittenhouse and Pikesville have different mashbills. If you go back in history a few short decades, Rittenhouse was made by Continental Distilling in Philadelphia as a higher-end Pennsylvania-style rye. Pikesville was made by Standard Distillers (I think?) outside Baltimore and was a higher-end Maryland-style rye. While both are now made by Heaven Hill, Maryland-style and Pennsylvania-style ryes often varied from one another in mashbill and flavor.
Yesterday I went down to Baltimore to a liquor store and while I was there (Maybe a half-hour), at least 4 bottles of Pikesville flew off the shelf. I was amazed at the pace at which it seems to be sold down there. The bottle I had of Pikesville wasn't too impressive, but I think I'd have to go back and try it again because at the time I was really into the milder, sweeter wheated bourbons. I LOVE Rittenhouse BIB. Next time I'm down in Baltimore I may pick up another bottle of Pikesville. I just wish it was 4-6yo and 86 proof!