The higher output numbers come with GM announcing the SAE certified figures. GM's dyno graph is below and yes that is a peak of 650 lb-ft of torque at 3600 rpm. That is 40% more peak torque than the LS7 7.0 liter V8 in the C6 Z06 and 7.5% more torque than the C6 ZR1's supercharged 604 lb-ft.
Jordan Lee chief engineer for GM small block V8 engines stated, "Torque is the pulling power of an engine and the LT4′s abundance of it at every rpm in the engine’s speed range helps the 2015 Corvette Z06 accelerate quicker and respond nearly instantaneously. It’s the very definition of power on demand.”
He is not wrong. Say hi to the most powerful car GM has ever produced.