Below are the Handbrake results from a few Macs I had access to. I'm not sure where it went, but I also have an H.264 USB accelerator somewhere that I could test with. Sadly no ffmpeg support ever materialized for it (CrusherHD). I was hoping to get this working on my ReadyNAS for better AirVideo transcodes.

Quote:
Start with Handbrake preset AppleTV 2 (720p)
Change frame rate to "same as source"
Audio - audio track 1 AC3 passthrough - eliminate other track
Text - keep all sub-picture content, un-check forced and burned

2012 Retina MBP (2.6GHz i7 3720QM Quad Core) - 0:55 encode time, 48.89 fps, 66.4MB
2008 Mac Pro (2.8GHz Xeon E5462 Dual Quad Core) - 0:57 encode time, 47.81 fps
2011 MBP (2.5GHz i7 2860QM Quad Core) - 1:12 encode time, 37.15 fps
2010 Mac Mini (2.4GHz Core 2 Duo P8600) - 5:04 encode time, 8.83 fps

Also tried it in Quicktime X on the Retina MBP, using the normal 720p with Intel Quicksync. Also 0:55 encoding time, but half the CPU usage. Output file 86.8MB

Quicktime X with the Apple TV 720p preset took a little longer at 1:03, similar near max CPU usage as Handbrake. Output file 81.1MB