Most recently I would have sided with using the 160ttsx especially if it is a Barnes. However, after running calculation across Hornady's ballistic program (assuming 1602900 and 2102600), the only benefit IMHO in using a 160 gr ttsx over the 210gr ttsx is the 1.1 less drop at 300 and 2.6 less drop at 400. But take a look at the velocity and energy. At 300yds the velocity is almost idenitical but the energy is approx. 400 ft/lbs difference.
I believe you could wack Elk all day long with the 160gr ttsx but the 210gr ttsx gives a little extra insurance at least on paper.