[Openchrome-users] CN400 vs. CN700 vs. next best option?

[Peter Carmichael]

I've been using CN400 Epia SP8000 boards since they came out. 
Openchrome has been fantastic for these boards with CPU usage down at
~3% for xine playback of SD DVD MPEG2 and similarly low utilization for
Mythtv playback.  I've run test mpeg2 files at HD resolutions and the
hardware copes just fine.  ~15% utilization for 720p. ~24% for 1080i. 
Typically all my output is at 1280x720 over VGA.

The SP boards aren't available any more so I'm looking at CN700 boards. 
My first build for an Epia CN10000 is not as impressive.

VLD XvMC isn't working (apparently) in MythTV 0.21.  xine is working
(using -V xxmc and XvMCW) but is showing 20% cpu for SD material.

My build is gentoo and I haven't gone back and recompiled it yet with
optimised CFLAGS for the C7 cpu (msse2 msse3) but so far I'm not seeing
anything special in the CN700.  The kernel has been updated for the C7.

Any ideas why I am seeing such a performance drop off with the CN700/C7
combination?