1) Are you using CUDA? If not then you're really not using the capabilities of the Ion platform in Revo, which is a waste. I don't have the device in question but I'd venture a guess that Ion + dxva acceleration is still less taxing than CoreAVC & CUDA.
2) Can you verify that M2t file (I'm assuming is off some camcorder of yours) has any aspect ratio spec in it? Say, check it with MediaInfo.
CoreAVC has arguably the best CUDA acceleration available. Generally, custom CUDA code tends to perform better than general-purpose DXVA acceleration, if the developer bothers to actually code the CUDA paths well and properly. CUDA is more powerful and flexible.
The problem with his M2T files is that the HDV compressor uses a special custom PAR (Pixel Aspect Ratio) in order to have 1440x1080 equal a 16x9 display aspect ratio (PAR of 1.333). The M2T file format doesn't have a lot of metadata capabilities to include a specific PAR as part of the file header, it can only specify widescreen vs. 4x3. Still, the M2T coming off of the camcorder should be flagged as widescreen, which would make it display correctly. Unfortunately, lots of camcorder software applications don't do this properly, so my guess is that his M2T files aren't flagged as widescreen.
I'd venture a guess that VLC and MPC-HC have special code to deal with HDV M2T files, and when they see a 1440x1080 M2T file, they enable 1.333 PAR even if the widescreen flag in the file is missing. This would make "true" 1440x1080 (square pixel) content display incorrectly, but those files are probably quite rare as there is no standard for 4x3 1080p video.