Despite a company history of leading the industry in graphic fidelity, id Software's upcoming Rage -- while still among the best-looking games out there -- intentionally prioritized framerate over graphics in development.According to the company's legendary programmer John Carmack, that decision was a "hard-fought battle" internally."I made the conscious decision that the user is going to get more value out of running at a higher framerate than me making the pixels pretty," he told Gamasutra as part of a larger interview."I think I could have made the game look better at 30 hertz. We could have had some more design freedom," he admits, though he says the decision to focus on keeping the game at 60 frames per second will look better to just about everyone, including those who can't tell the difference between 60 and 30."Most people get at least a subliminal feel about it," he says. "It's more responsive. It's crisper. It's smoother."But framerate perception has its limits. Carmack tells us he conducted a number of experiments to see if players responded to a doubling of framerate, having them play a demo in both 60FPS and 120FPS."Interestingly, almost nobody can tell the difference between 120 and 60," he says, adding that this "means that we've got this benefit curve on here, and 60 is kind of right at the knee."This, in addition to technological advances like the iPhone 4's nearly print-level resolution, is "cool thing that in many ways, we are approaching sort of the biological limits of what betterness we can display," he says.More insight from one of the most fascinating figures in video game development is available in our full interview