If you go by the numbers, the Leopard 2a6 actually is faster, more efficient, has a more powerful gun, and is better protected than the M1a2. The US Army is currently looking into adopting Rheinmetall's L/55 120mm gun to increase the lethality of the Abrams.
Max operational range:
Leopard 2a6: 350 miles
M1a2: 250 miles
Max top speed:
Leopard 2a6: 42mph, 34mph cross country
M1a2: 42 mph, 30mph cross country
The L/55 gun gives the Leo2a6 the ability to kill other tanks at a range of 4km rather than the 3km of the Abrams M1a2.
The German army has been upgrading their tanks with improved protection against IEDs and shaped charge weaponry.