Rollie Free's Vincent was not on the street. It was a Bonneville salt bike.
In fact, virtually no Vincents were on the street in the late 50s and 60s. Vincent went out of production in 1948 or so.
And Ariel Square Four, at 1000cc with 7:1 compression and 42hp vs the 900cc Sportster's 55hp. The Sportster was King of the Road from 1957 until the late-60s and the emergence of the "Superbike" with the Norton 750/850s, Honda 4, Kawa triples etc etc.
And no Vincent ever made, ever went anywhere near as fast as this Sportster:
"In 1970, Cal Rayborn piloted a Sportster-powered streamliner across the Bonneville salt flats to a world motorcycle land speed record of 265.492 miles per hour. The long, low, cigar-shaped missile in which Rayborn became the fastest man on two wheels has frequently been referred to as the “Rayborn streamliner”
This Sportster was THE FASTEST MOTORCYCLE IN THE WORLD in 1970.
Yeah, they're shit now.... But 40 years ago they were HOT!
Notice "Il Douche'" compares the performance of factory sponsored Harley streamliner in 1970 to that of an unfaired basically stock privateer Vincent in 1948. But the (Heavily modified probably-nitro-burning factory sponsored) Sportster was THE FASTEST MOTORCYCLE IN THE WORLD in 1970!
If they weren't morons they wouldn't ride Harleys.
Incidentally, doesn't that Vincent remind you of a new Confederate?