I was building up an S-Class contender from each of my favorite manufacturers. My short list:
Ferrari F40
Jaguar XJ220
Ford GT
Viper Competition Coupe
Corvette C6 Z06
Porsche (maybe one of the 911 variants or the Carrera GT)
and a couple of Japanese cars that I haven't thought of yet. When built out to S998, the cars above all came out pretty close. There are a few that I haven't included that would probably do extremely well, but I'm not sure they would be good for balance. Cars like the Enzo, Pagani, CLK-GTR and Saleen haven't been considered thus far, so it might not be that bad, but my fear is that they will outclass everything else.
Basically I love the idea of the supercars from the major manufacturers throughout history doing battle with cars descended from the greats. The lack of history could be reason enough to exclude the Pagani and the Saleen...
I originally got interested in S-Class because my Ferrari F40 couldn't fit into A-Class. The lowest it will go is PI 851 dadgummit! So I went ahead and built it out for S-Class and was rewarded with a pretty darned decent car for its class. I started thinking of other cars that needed a home for one reason or another. The Jaguar XJ220 doesn't work in anything lower than S so I built it next. It posted numbers VERY close to the F40. To complete the European collection I built out a Porsche 959 and discovered again that it isn't really good at much of anything.
Disappointed, I decided to bump the Ford GT that I had squeezed into A-Class up into S-Class. The numbers were again VERY close to the F40. To me, this was appealing because the GT40 was developed specifically to kick dirt in Ferrari's face. It was only appropriate that the new Ford GT set its sights squarely on the prancing horse, just like it's daddy so many decades ago.
A few days after that flurry of builds I got sick of American people telling me that all American cars are crap, so I built out a few more contenders from the states. The latest model Viper, the Viper Competition Coupe, the C5 Z06 and the C6 Z06. The GTS ACR Viper had already found a home in A-Class. The latest model Viper doesn't look the part of a GT race car with it's rag-top, but does post impressive numbers. The nicest thing about it is that, unlike the Competition Coupe, it offers adjustable aero. The Comp Coupe obviously should have adjustable aero, but c'est la vie.
The C5 Z06 is currently an A-Class experiment with promising results. I can't drive it all that fast, but it's got the potential. The C6 Z06 is probably my only S-Class build riding on stock wheels. It just doesn't take much for this car to go over 998, so I had to look for points wherever I could. I haven't put much seat time into either car, but everything is in the right place and pointing to strong performance.
What worries me is that the heavies of S-Class are going to make my experiments look sub-par. I consider the heavies to include:
Saleen S7
Mercedes CLK-GTR
Pagani Zonda C12
Ferrari Enzo
I think I've finally got the above unlocked so I'll be building examples out soon.
Bimmer's edit: Here is the set of restrictions we currently have set up.
Supercars
The Cars:
Ferrari F40
Lamborghini Diablo GTR
Pagani Zonda
Mercedes SLR
BMW M3 GTR
Porsche Carrera GT
Ford GT
Viper Competition Coupe
Shelby Series One
Honda NSXR-GT
Nissan R390
Jaguar XJ220
TVR Sagaris
Koenigsegg CC8S
The Regulations:
Cars must have a PI of S998 or below.
Cars must use Slicks (Racing level tire upgrade)
Cars must remain RWD.