If 300W is the PCI-e limit i dont see it being an issue. Under current protocols for meeting specs, i dont think any game coding would be 'valid' that did that. The design spec is after all 300W. Why design games that require more power than a single card can meet by specification. Given the console domination of gaming design, we're still not even getting DX 11 up to a good standard yet. In the future i dont see it happening either as the manufacture processes shrink. As for the car analogy, most super sport production cars have speed limiters (150mph for many BMW/Mercedes etc) built in, so we do buy cars with metaphorical chokes built in.