Turbo boost works depending on workload.
In single-threaded workload (1 core active) i7-6700 will boost to 4Ghz,
with 2 cores active - it will boost to 3.8Ghz,
with 3 cores - 3.6Ghz,
with 4 cores - 3.4Ghz.
So it depends on game you play. If game utilizes only one core, then cpu will boost to 4Ghz.