[mythtv-users] MythTV, smooth playback on 3ghz, and 1080i?

[Rob]

Got a question for those of you running 3ghz processors [b]without[/b] XvMC
decoding 1080i and deinterlacing successfully.  What is your secret?  I've
tried 3 different machines with 3ghz (or close to it), and none of them come
anywhere close to being able to do 1080i video smoothly in Myth.   I'm
running Deban and have built Myth and have tried optimizing it for the
processor I'm using and such, and it never seems to matter.    The OSD is
the worst offender by far, when that is up it's jerk city.   1080i video
sometimes managed to get by at full framerate and sometimes doesn't, it's
inconsistent.   

Now, I can enable XvMC and everything plays back perfectly smooth, but as
noted by most FAQs, the OSD is in black and white, sometimes flickers badly,
and causes the screen to jerk.  Once it goes away everything works okay.
Most of the FAQs and posts I've read from people seem to indicate a 3ghz
processor is plenty of horsepower to do 1080i without xvMC.  Why does it
perform so badly on my system?   I think perhaps if I can find my
performance problem even xvMC will work work better. 

I apologize if this is in a FAQ or has been discussed ad nauseum, but I've
been at this for over a week and haven't found anything.

Video card is a FX5200
Nvidia 7676 driver
Currently testing with P4 3ghz, but have also tried Athlon 2800+

Things I've tried:

Open GL overlay (does this even work with NVidia drivers?)
MPEG2Dec decoder (seems to make it worse)
Various deinterlace modes - performance is just as bad with it "off"
Sync to video
Myth "stable" version 18.1 and the SVN head

Any help greatly appreciated.