Hmmm . . . Sounds like you're doing everything right. If you haven't spent a huge amount of time tinkering with the derailleur height and/or the upper limit screw, I'd probably give those another shot. FD adjustment can be really finicky sometimes. One other thing you might tinker with is the derailleur angle. As you know, the outer cage plate is supposed to be parallel to the chainrings, but sometimes the plates aren't entirely straight and a little deviation from the general rule is helpful. If I've got this right (and I might not), angling the front of the cage ever so slightly to the outside might allow a quicker upshift while helping to prevent an overshift. Unfortunately, this adjustment will have the opposite effect when you downshift. But if it's only a very minor adjustment, you might get away with it. I'm afraid that exhausts my limited store of ideas. Best of luck to you!

Edit: I'm betting you've already checked this, but just in case you haven't -- have you got the chainline right? Since the derailment is happening when you're in the middle cog on the rear cassette, this seems unlikely to be the issue, but I'm grasping at straws, now.