The RC51 was the successor to the RVF750R (RC45) which was the successor to the VFR750R (RC30) and was built to beat Ducati at their own game in the superbike world championship. In the US the RC51 was called the RVT1000R, in the UK and Australia it was called the VTR1000 SP1 or SP2. The VTR1000 Firestorm (SuperHawk in the US) is a different bike, not intended for racing homologation but designed for the street. The VFR800 was a sport touring bike, very different from the RC30. The NC30 and NC35 VFR400s were sold legitimately in the UK after several years of grey import but were unreasonably expensive. My 1991 VFR400 was originally sold in Japan (1991 was JP-only), was imported to the UK (grey) and made it to the US as soon as it was 25.
We didn’t see too many 400s in the UK, I think they were all unofficial imports but was a long time ago to remember.
Mate has a VTR1000 Firestorm if that’s what you meant? Outstanding bike, extremely hard to keep under 100mph, fuel tank was genuinely stupidly small. The SP1 and 2 were the superbikes IIRC and different beasts to the Firestorm, never had the pleasure of riding one of the superbikes. But yes, a Duke 998 over an SP1 I think.