I'm not sure if I understand your question correctly. kx provides shared libraries to make R and q talk to each other. The specific approach I followed used a shared library that brings R into the kdb+ memory space, meaning all the R statistical routines and graphing capabilities can be invoked directly from kdb+. Using this method means data is not passed between remote processes.
In other words if you put q ontop of a R DataFrame would you expect the same performance? Or if you ran R ontop of K.