Agree, nothing wrong with a 300 SE/SEL - great cars. They do pull well, and they are helped in that they have a 3.46 rear gearing as opposed to the long gearing of the 500 cars which have a tortoise like 2.24 rear end.
If speed is an issue, then really only the 560 SE/SEL/SEC with Option 822 (increased power output) is an option. The 560's had a better rear diff with a 2.65 gearing.