This is my opinion in-summary
2006-2009 Rover Sport and FFRR
NA 4.4: Barely adequate power. It is quite a dog for today's standards. Passing is a chore as well as taking someone at a light for a quick lane change.
SC 4.2: 0-60 in a little over 7 seconds. Just adequate for today's standards. Fine for doing most things. Drinks gas badly- 12-14 MPGs overall. The SC compressor sounds awesome.
It passes from 50 to ??? pretty well.
2010-2013 Rover Sport
NA 5.0: 0-60 in around 7 seconds. If I lined up the 5.0L vs the 4.2L SC, I bet the 5.0L would take the SC. It's much better on gas as well. 18-20 Em Peh Gehs highway. (Ron Burgundy)
This NA 5.0L likes to rev to make good power. Sounds better naturally in the cabin. The engine is more fun overall. It likes to play and wind up.
SC 5.0: 0-60 in probably a bit less than 5 secs. Owning both, it makes it feel like your NA 5.0L is standing still. Crazy power at any speed for a car this size.
Huge torque/horsepower instantly. Also better on gas than the 4.2L SC, but still not good at all at like 16-17 Em Peh Gehs.
You can barely hear the supercharger, but it's a much higher pitch (higher spin speed?) than the 4.2L SC "Howler"
I am not trying to offend anyone with a 4.4, but that would be the absolute last engine I'd choose in the Rover Sport for daily driving. I had an LR3 loaner for a week and had to work that engine pretty hard to just drive it normally.