[mythtv-users] HDTV modeline frustrations

[Brian Foddy]

I've been playing around trying to get the
best modeline combos for my HDTV.  Everything
I've read says its a tedious process, that's
an understatement.  First, the hardware I have.

Hitachi 43FWX20B TV, cabable of 480p/540p/720p/1080i
according to the specs I've seen (which aren't
terribly detailed).
Nvidia FX-5600 graphics card.
KDS vga-component converter.

I've read several faqs/how-tos including
http://www.avsforum.com/avs-vb/showthread.php?s=&threadid=33207
http://www.sllug.org/how-to/linux-htpc/video_card_configurations.html
and others.  And I've loaded the powerstrip windows program
on the same machine.

Where I'm at...
480p.  No problems.  Image somewhat overscanned
but usable.  I haven't found any 16x9 480p resolution
that works yet (something like 848x480).

720p.  This will probably be my eventual goal.
Using the standard HDTV settings I've seen on the
web and powerstrip, the image is stable, but much more
overscan than I'd like.  I estimate 50+ pixels on each 
right/left side, and another 30 pixels on each top/bottom
side.  ie:  In windows, I can't see any of the first icon column.

540p/1080i.  So far I haven't found any setting that 
comes close to syncing with the TV.  Clearly my 
external HD tuner has no problem giving the TV a 1080i
signal.  I haven't spent as much on these resolutions yet,
but I've had the least luck on them too.

Questions:
1.  My primary question is about Dot Clocks.  As I work through
the adjustments and formulas, most sites seem to assume the
clock is constant.  Its nearly impossible to make significant
improvements in overscan (720p) keeping the clock constant.
The standards for 720p at 59.9Hz have a clock around 74Mhz, I found
it takes a clock 80-85Mhz(59.9Hz, 44.9Khz) to make significant 
improvements in my overscan problems.  But I don't see ANY guidelines 
on how to judge if this is safe.  The HDTV seems to show a stable
picture, but I've only run it for short periods of time.
I can't find any detailed specs for the TV, and most faqs/how-tos
don't talk about the clock rate much.  Thoughts?  
What symptom would I see if I'm over-driving the clock on the TV?  
Is 74Mhz some assumed standard I should just not touch?  Where does 
that value come from?
I don't think my HDTV tuner at 720p has this much overscan?

2.  The 540p/1080i problems?  Not really far enough
to ask good questions, but every attempt I make has the
TV trying to tune 480p (according to its status) and making
a horribly unsynced picture.  Mostly using powerstrips
standard HDTV settings.  I've never gotten the TV to
even show the 1080i status yet.  Thoughts?

Lots of stuff here, thanks for reading it.  Hope someone
can help.

Brian