Mercedes-Benz' costliest convertibles are two-seaters with a power-retractable metal hardtop. Four models are offered. The SL500 has a 302-hp V8. The high-performance SL55 AMG has a 493-hp supercharged V8. The SL600 has a twin-turbo V12 also rated at 493 hp, but with more torque than the SL55's V8. The SL65 AMG has a 604-hp twin-turbo V12 and specific styling touches. All have automatic transmissions: a 7-speed on the SL500, a 5-speed on the others. All include a manual floorshifter, with AMG versions adding performance programming and steering-wheel shift buttons. Standard are traction/antiskid control and Mercedes' ABC active suspension designed to reduce cornering lean. Also standard are "by-wire" antilock brakes that can modulate brake pressure to each wheel. All include head- and torso-protecting side airbags, driver knee airbag, and a rollover bar designed to deploy in an impending tip. Also standard are navigation and assistance systems. Options include adaptive cruise control. Among changes for 2006: a keyless entry and starting system is standard on the SL600 and SL65 but remains optional on SL500 and SL55; run-flat tires are newly available for SL500 and SL600; and SL55 is available with a $14,000 AMG Performance Package that includes exclusive exterior trim and a top-speed governor of 186 mph vs. other models' 155 mph.