Encoder settings in whipeclientsink

I use whipeclientsink and I am wondering how I can tell the encoder to use more CPU. It seems to be using something like fast x264 profile and the quality is not good, even at 10mbit/s.

My pipeline is detailed here: Auto reconnect in whipeclientsink - #22 by kuon

I tried both x-264 and x-vp8 video caps.