I definitely gonna get a 4U instead of a 3U. 3U is just too sluggish for my doubles games. For my normal game pace, the difference in speed between a 4U head heavy and 3U head light is marginal. Objectively speaking, if your games in general are fast paced, the disadvantages of 100zz will show itself pretty soon. With that being said, 100zz is made to suit both doubles and singles alike, it has qualities that help in doubles despite its head balance that rivals the AX99. Also, 100zz has a completely different hitting feel compared to NF800, a lower thump.