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Actually, we are not allowed to give opinions, but I can tell you what the experts on other websites that review cars say.
2010 BMW M6 What Edmunds SaysThe 2010 BMW M6 has one of the best engines on the planet. If you're down with the styling, high-performance coupes don't get much better for $100,000.ProsDelectable 500-horsepower V10, excellent handling, relatively supple ride, high-quality cabin, great seats.ConsOutdated single-clutch SMG automated manual, uncharacteristically numb steering, polarizing styling
2010 BMW M6 Features & Specs Base Coupe(5.0L V10 7-speed Automated Manual)
Fuel economy: 11 city/17 hwy mpg
Torque: 383 ft-lbs. @ 6100 rpmHorsepower: 500 hp @ 7750 rpmhttp://www.edmunds.com/bmw/m6/2010/features-specs.html
2012 BMW M3 Coupe What Edmunds SaysThe 2012 BMW M3 might be the best all-around car for the driving enthusiast. To the track, the office or day care, the M3 handles it all with purpose and style.ProsSublime high-revving V8; otherworldly handling; relaxed highway ride; convertible's sleek retractable hardtop.ConsLimited interior storage; relatively cramped rear seat.Fuel economy: 14 city/20 hwy mpg
Base Coupe(4.0L V8 6-speed Manual)
Torque: 295 ft-lbs. @ 3900 rpmHorsepower: 414 hp @ 8300 rpm
2012 Cadillac CTS-V Sedan What Edmunds SaysThe 2012 Cadillac CTS-V delivers a combination of world-class performance, style and value that's tough to beat.ProsStunning acceleration; superb handling; distinctive appearance; elegant interior design; reasonable price tag.ConsUncomfortable and unsupportive standard seats; feels big on tight roads; compromised rear visibility.Fuel economy: 14 city/19 hwy mpg
2012 Cadillac CTS-V Sedan Features & Specs
Base Sedan(6.2L V8 Supercharger 6-speed Manual)
Torque: 551 ft-lbs. @ 3800 rpmHorsepower: 556 hp @ 6100 rpmhttp://www.edmunds.com/cadillac/cts-v-coupe/2012/
2012 Cadillac CTS-V Coupe
What Edmunds SaysThough its practicality is disappointing, the 2012 Cadillac CTS-V Coupe delivers a combination of world-class performance, style and value that's tough to beat.ProsHead-turning design; stunning acceleration; athletic handling; a relative bargain. ConsPoor rear visibility; limited headroom with sunroof; compromised trunk; uncomfortable and unsupportive standard seats
Fuel economy: 14 city/19 hwy mpg
2012 Cadillac CTS-V Coupe Features & Specs
Base Coupe(6.2L V8 Supercharger 6-speed Manual)
Torque: 551 ft-lbs. @ 3800 rpmHorsepower: 556 hp @ 6100 rpm
They didn't have a review for the 2012 m5, hold on 1 moment.
As far as performance goes, the 2012 BMW M5 has the highest numbers and the 2012 BMW M3 Coupe the lowest. The 2 Cadillac's are the same are in the middle and the 2010 BMW M6 is just below that. I would say the best performance has to be with the 2012 BMW M5.
2012 BMW M5Torque: 680 ft-lbs. @ 5,750 rpmHorsepower: 560 hp @ 6,000-7,000 rpm2010 BMW M6Torque: 383 ft-lbs. @ 6100 rpmHorsepower: 500 hp @ 7750 rpm2012 BMW M3 CoupeTorque: 295 ft-lbs. @ 3900 rpmHorsepower: 414 hp @ 8300 rpm2012 Cadillac CTS-V SedanTorque: 551 ft-lbs. @ 3800 rpmHorsepower: 556 hp @ 6100 rpm2012 Cadillac CTS-V CoupeTorque: 551 ft-lbs. @ 3800 rpmHorsepower: 556 hp @ 6100 rpm