When I saw Equus in London (with Dan Radcliffe, but not Richard Griffiths, who was out sick--boo!) I sat midway back in the side Orchestra (or Stalls, as they call it). It was OK. I don't know if they'll be using the same staging, but most of the action takes place in the center of the stage, so you don't miss anything if you're on the sides. Mezzanine Center will probably get you the best overall view of the stage, obviously, but if you want the close-up, ahem, *view* than you might want the Orchestra seats close to the stage.
Coach Bob knew it all along: you've got to get obsessed and stay obsessed. You have to keep passing the open windows. (John Irving, The Hotel New Hampshire)