The important thing about the "faster/higher" WW2 bomber and loss rate is, that the concept was proven by the Mosquito, hugely reduced loss rate to defences in the night bombing role due to speed and height. The German night fighters were always vulnerable to being too slow to achieve kills. The Do217 night fighter was phased out due to this and, the Bf110G would have been seriously reduced in effectiveness by any increase in the speed or altitude capability of the night bombers. I suspect that more effort could have been made to achieve higher/faster but it wasn't and the bomber crews paid a heavy price.
OAP