Ehm, if your server runs a reasonable modern x264, you should get significantly lower bandwidth at "transparent" quality compared to what the GPU's hardware enc

Ehm, if your server runs a reasonable modern x264, you should get significantly lower bandwidth at "transparent" quality compared to what the GPU's hardware encoders is even capable of reaching. The reason there being that the hardware encoder can't use some features x264 implements sufficiently fast to make them worthwhile to use at that sort of time investment. Please don't try to measure lossy-anything-calculation by speed alone, always make sure that the required quality can even be reached, and even if, that it still exhibits the performance benefits, even after you tune these features up far enough.