An hour is a very tight connection, given how easily it is to be delayed getting into LHR. If you don't have status/fast track access I wouldn't attempt it, go for the longer connection. You never know if you will and up at a bus stand and have to wait for the buses to come and take you on a circle tour of the airfield before you eventually end up at the terminal.

Not that fast track security can be all that fast at times either....