Packing the Corvette Z06’s supercharged LT4 engine into the opulent Cadillac CTS-V was no small feat for GM’s engineers. But they somehow managed to do it, in the process creating the most stupid-powerful luxury sedans on the planet, a velvet bullet of performance and pleasure all in one. Yet even though it packs more horsepower than its rivals and even its predecessors, there’s no such thing as excess at the apex of the luxury food chain.

According to recent rumors, 640 horsepower isn’t even the final form of the CTS-V. The unnamed source doesn’t cite specific numbers, only saying that 640 isn’t the end game for GM’s luxury division.

Outfitted with other performance features, like Magnetic Ride Control, Brembo brakes, and a carbon fiber hood that lowers the curb weight, the Cadillac CTS-V already offers more go-fast goodies than rivals like the Mercedes E63 AMG. But you can be guaranteed that its German rivals are readying answers to the CTS-V of its own, so if this rumor is true, it seems that GM is dedicating itself to staying on top.

It might not just be the Germans GM wants to take on though. Crosstown rival Fiat-Chrysler has their pair of 707 horsepower muscle machines, the Dodge Charger and Challenger Hellcats. These sit at the top of the food chain as far as overall output goes, and now could very well be the last time such egregious amounts of horsepower can be obtained from combustion-only production V8s. It’s now or never for the horsepower wars, and apparently GM hasn’t hit its limits with the LT4 engine.

We wonder what that means for the Corvette Z06 as well?