I wouldn't change the amount of FBS unless it is absolutely necessary for the experiment. Several types of studies use serum starvation (lowered amounts of FBS than prescribed) to induce specific results, such as to study environmental stress, protein expression, and is known to arrest cell cycles. Since cell cycles are very important to differentiation, I would surmise that it could have an affect. I hope this helps!
Pirkmajer S, Chibalin A. Serum starvation: caveat emptor. American Journal of Physiology - Cell Physiology. 27 July 2011 Vol. 301 no. 2, C272-C279 DOI: 10.1152/ajpcell.00091.2011