Tried the R10 and failed with it - tires quit on the last lap, and I lost nearly a minute (had a 34-second lead at the start of the lap, and lost by 24 seconds, all that time seeming to be lost in the last half of the lap.
)
But I then tried the '01 Audi R8 (the open-top LeMans racer, not the sport coupe that just came out a couple years ago). Big turbo, 880-some HP, minimal downforce, top speed on gearbox set at 255mph, started on Sports Softs (yes I did), kept 'em on 'til end of L5, swapped for Racing Intermediates, and went on to the end on those. Won it by just over 7 seconds with this.
Others have won with the Peugeot 908 HDI FAP (very few, but at least one person has), the Toyota GT-ONE, and others.
Meanwhile, if anyone needs to borrow a Chappy 2J, just hit me up. "Kwicko" on PSN, and I've got one set to shared status. Or let me know what else you'd like to try it with, and I'll see what I can do.