Apparently the two “Super-“ versions do share the same performance. Maybe the SC does produce the same 510 horsepower as the SS and not the advertised 470. It’s actually faster than the Cadillac CTS-V and especially the Mercedes-Benz E63 AMG from before the Biturbo era.
XJL Supercharged:
https://www.motortrend.com/news/2011-motor-trend-car-of-the-year-contender-jaguar-xj-9426/
…versus…
XJ Supersport:
https://www.caranddriver.com/reviews/a15127084/2011-jaguar-xj-supersport-test-jaguar-xj-review/