Complete noob to high-end audio. Best price/performance for TF2?

I don't see why Team Fortress 2 would have different requirements out of a competitive headphone than other FPSs.

You should be fine with an AD700 (if competitive positioning is all you're looking for and you don't need bass presence) and a $50 X-Fi Titanium. Point ALchemy to the TF2 installation folder, enter "snd_legacy_surround 1" in the console, set up CMSS-3D Headphone accordingly, and you're good to go. The only downside is that at typical AD700 prices, you're going to go above $100, but still well under $200.

On the other hand, the SR850 would be cheaper than the AD700, but I've never tried one of those.

I was in a TF2 clan for a while and I can tell you that Source is pretty forgiving about whatever headphones you have. Though, TF2 isn't really one of their more optimized games in terms of audio. L4D2, and Portal 2 are, though. Portal 2 is one of the best sounding games I have.

Audiotechnica AD700

Unless your head is like a peanut and tiny.

I like gaming with Grado's but the only problem is they get uncomfortable for long sessions.

Q701's seem like overkill for just gaming.

Whatever you go with, I'd recommend something that has a wide sound-stage. It's way out of your price range but when I bought my Heir 4.A's I suddenly found that the wider sound stage gave me exceptional directionality in L4D2. I was constantly picking out special infected as they spawned because I could hear them so clearly and whether they were to the left or right (after that it became a bit of guessing as to up or down). I got accused of hacking on more than one occasion because of them.

To that end, Ultimate Ears 700's have a good sound stage for around $150. With Comply Foam tips I've found I can use them for a good few hours. One potential problem with IEMs and computer gaming is that it's easy for things to get loud, which could damage your hearing. Keep that in mind if you go this direction.

At the $220 level Denon AH-D2000's are extremely comfortable with a good sound stage (and great bass). There was a time playing Bad Company 2 where I chased a guy around a house listening to his footsteps. Another where a take exploded next to me and my headphones vibrated. They are exceptional. You might be able to get them for cheaper as they're now a few models behind the current.

The mentions of Grados is a good one. The SR80i has a retro kind of look but amazing sound for the price. They'll run you around $100. One warning about open-back headphones is that they will block out no sound in either direction. You will be able to hear everything in the room around you and anyone in the room will be able to hear what's going on in your game.

Might want to take a look at the Sennheiser HD518. It runs for around $130 but is a full-size can so it sits around your ears (not on) and is supposed to have a very wide soundstage. It's open backed so best used in private but beyond that it might fit the bill quite well.