All Games Hang Briefly Then Recover, Desktop Dual Boot Windows 7 & OSX?

All games I've played recently (both single and multiplayer, whether through Steam, Origin, or standalone, internal or external drive) occasionally freeze up and then recover. It usually lasts only a couple of seconds. Example games:Dragon Age II (singleplayer, through Origin, external drive) League of Legends (multiplayer, internal drive) Raiderz (multiplayer, internal drive) Jade Empire (singleplayer, through Steam, external drive) Skyrim (singleplayer, through Steam, external drive) Dark Souls (multiplayer, through Steam, external drive) I haven't checked every single game on my system, I can try others if that will help diagnose the problem.

My systemMac Pro 2009, dual booting Windows 7 Home Premium, SP1, 64-bit OS with Boot Camp. Problem is with Windows 7 boot. 2 Quad Core Intel Xeon CPU - W3540 @ 2.93.GHz 3.06GHz 8 GB RAM ATI Radeon HD 5870 Some games are on an external drive. There does not seem to be a difference in how often games on internal vs external hang. Things I have already triedEverything on the troubleshooting thread except relating to DirectX 11 (these games aren't using it on my current settings) Everything on this "games hang briefly but periodically" thread Alt-Tab to Resource Monitor after a hang. No strong correlations found. Some spikes in Queue Length, some in CPU, nothing I can identify as obviously related. Reinstalling Windows & games with a fresh Boot Camp partition (When all else fails... no good though.) Upgrading my graphics card (I wanted to do this anyway, hoped it would help... games are a lot prettier, but no dice on the hanging problem) Order of events:No problem for ~3 years of use Installed Dragon Age II, needed to update graphics driver for it to run. At the time I had NVIDIA GeForce GT 120. I did a fresh driver install, initially I thought this might be the reason because it could have cleared out something from Boot Camp's special drivers. DA2 running, is first game to show hanging problem. Mainly happens at start of battle. Noticed next in League of Legends.First attempt at troubleshooting. Updated all drivers, Windows 7 updates, etc. Re-installed Windows in a clean Boot Camp partition, since (as noted) I thought I might have messed up some of BC's drivers. No improvement. Got tired of my overall crappy graphics and got a new graphics card, hoping it would also fix the hang problem. New card: ATI Radeon HD 5870. Games are super pretty! Still hang. Followed all of troubleshooting and hanging thread advice, minus DirectX 11 settings (since not using 11--even DA2 is set to 10). Still no improvement. I know my way around a computer but I'm no expert, and this is over my head. My only remaining theory is that it's something about running on Boot Camp--but it was fine for 3 years.