According to mygranturismo.com, the top 10 are...
Jay leno tank car 3500 kg
Land Rover Range Stormer Concept '04 2500 kg
Dodge RAM 1500 LARAMIE Hemi Quad Cab '04 2390 kg
Silverado SST Concept '02
by Chevrolet (2002, USA) ??← 474 →
?? → 95,000 Cr
S - 8 489 HP - 2268 kg
655 Nm - FR 160 3 3
SSR '03
by Chevrolet (2003, USA) ??← 406 →
?? → 44,560 Cr
S - 2 295 HP - 2248 kg
448 Nm - FR 98 1 3
SVT F-150 Lightning '03
by Ford (2003, USA) ??← 442 →
?? → 35,050 Cr
S - 4 387 HP - 2132 kg
621 Nm - FR 135 2 3
SL 600 (R129) '98
by Mercedes-Benz (1998, Germany) ??← 464 →
?? → 210,270 Cr
S - 7 395 HP - 2029 kg
581 Nm - FR 145 6 3
SL 65 AMG (R230) '04
by Mercedes-Benz (2004, Germany) ??← 538 →
?? → 190,700 Cr
S - 13 614 HP - 2028 kg
1018 Nm - FR 226 2 3
RS 6 Avant '08
by Audi (2008, Germany) ??← 518 →
633 → 166,000 Cr
P - 10 582 HP - 2025 kg
662 Nm - 4WD 214 2 4
SL 600 (R230) '04
by Mercedes-Benz (2004, Germany)