If these spy shots are anything to go by, it seems that Mercedes are readying their G Wagon AMG models for an upcoming auto show, hopefully Detroit.Our spy photographers have just spotted two facelifted Mercedes-Benz G Wagon AMG models undergoing winter testing in Sweden, and we suspect one to be the G55 AMG and the other a G65 AMG.While the G55 AMG is relatively familiar with a seemingly less dramatic facelift, the G65 will be a very limited version featuring a biturbo V12 in that famous boxy body. Rumors abound that a limited series of 200 units will be priced at 250,000 Euros (approx. $325,000).The G55 AMG is likely to get the new 5.4-liter twin-turbocharged V8 with around 525hp and 516lb-ft of torque, while its being speculated the limited run G65 AMG will receive the S65 AMG\'s 6.0-litre twin-turbo V12 engine capable of 612hp and 737lb-ft of torque.Whatever power output it ends up with, enjoying it at full speed will be a costly affair even if AMG promises lower fuel consumption than the current version.New side mirrors, a revised grille, and a new front bumper with integrated coolers are all apparent, although the G55 seems to have only one cooler where the G65 gets two, one on each side of the bumper.We can also expect some LED day driving lights integrated in the bottom of the headlight unit, which are yet to be mounted on the prototypes. The brakes also look updated on this monster and the wheels benefit from a new design.On the inside there\'s a new instrument cluster, a new steering wheel and a sat nav screen atop the dash as seen on the new B-Class.The cars are likely to debut soon enough with Detroit in January or the Geneva Motor Show in March as possible destinations for their unveiling.