Tearing in video playback

Here is my set-up:

- XBMC Eden (MarcelG PVR Build 2012/07/27)
- Intel SandyBridge Core i7 3960 (3.8GHz, 6 Cores, 12 Threads, 15MB Cache)
- 16 GB DDR3-1600 MHz RAM
- 2xNVIDIA GTX 670 (SLI)
- ASUS x79 MoBo
- 90 GB OCZ SSD (OS)
- 1 TB WD (Data) + OCZ SSD (SSD Cache for Mechanical Data Drive via ASUS SSD caching)
- Synology 1510+ w/ 5x3TB WD drives w/ Synology DX510 expansion w/ 5x3GB WD drives

My above system accesses my NAS via wired gigabit (my brother and I wired my house so any connected systems do not have to rely on wireless). However, as I grab the CTV broadcasts of the Olympics I noticed that the MKVs are severely tearing, as is all of my other movies. I recently replaced my Radeon 7970 with the two NVIDIA 670s because of NVIDIA's Adaptive Vertical Sync technology. Since I moved my rig to my living room (TV) I was getting either tearing or stuttering in games, and the Adaptive Vertical Sync is just what the doctor ordered. However, since moving to NVIDIA now my video playback is spotty at best. I never had this problem with the Radeon.

I don't think the problem is lack of processing power (either CPU or GPU), and the NVIDIA 670 bests the Radeon 6970 in most tasks, so I don't think it is an issue of AMD/ATI vs NVIDIA. My best guess is that the NVIDIA GPU settings are different enough from the Catalyst settings to cause a problem in XBMC.

Things I've tried:

- Adjust frame rate - Doesn't help
- Syncing playback to display (sync on Audio) - This works pretty well for most things, but I will get slow down

Is there a WIKI page I'm missing with preferred options for NVIDIA cards? Any other thoughts? Thanks!