With the new Shimano 10 speed component compatibility - you are dealing with shifters and derailleurs but not 10 speed crank/chainrings. The new generation chains are not absolutely needed and the new brakes are not absolutely needed. I have serviced new bikes with new generation shifters/derailleurs and aftermarket brakes and 10 speed compatible chains. Best results may come with all Shimano components. But as always - a good mechanic can make different combos of components work very good.

A 6750 crank will work perfectly with 6600 components. 6650 works perfectly with 6700 components.