During the early release it was pretty smooth and the only trouble I had was targeting when faced with a large mixed group of mobs/players.

Ever since live though Fate's have been far too laggy to add any sort of meaningful contribution. What did help a little bit though is to completely turn off everybody else's spell effects at all times. Then set party members to show only some spell effects some times.

You can of course take it steps further and turn theirs off completely as well as your own...but I like seeing my own flashy spell animations.