I regard the 6.9 more as a Shadow 11 competitor.
6.9 slightly better techincally, the Shadow11 nicer coachwork, with a more recognised name for prestige.
The 6.9 has better performance and presumably better roadholding, and is a slightly scarcer car.
By today's standards of performance, neither are muscle cars, and with the way road laws are now policed, can't be driven as muscle cars anyway.