the way valve implemented multi core is pretty bad. the first core, renders the frame you would normally get. all the other cores render extra frames, but the data they use for that is based on the same data that the first core got, just extrapolated a little bit into the future. it is not based on the latest available data. that only happens once the first core starts rendering a frame based on data from the next tick.
it does make your game look smoother but besides that its basically useless.
this is why so many ppl feel like the game runs slow even with 300fps. 80% of that fps is useless frames