The 'rejects', for want of a better term, for Kaby Lake could be ones that top out at 4.8Ghz or 4.9Ghz. For a gaming chip—and let's face it that's all the i7 is good for these days—4.8 or 4.9Ghz is all you need. So, OK, you won't be able to hit 5.1Ghz or more, but you don't need to. 5.4Ghz is pointless. Your pushing enormous amounts of voltage into your CPU just for the sake of it. Performance will go up in all applications, but in gaming you'll be hitting a wall. And for the price of a 5.4Ghz 7740K I'd rather a Silicon Lottery 1700X or a 7800X.