7800 video card as an HTPC...?

My idea is to make one final upgrade to my Athlon64 3000+ 1 GB RAM AGP
system. I'll install a new 7800 GS video card on my aging rig. In
about a year or so, when the 7800 GS becomes obsolete, I can still
"retire" this system to work as an HTPC. Or at least, that's my
justification for spending $300 on an aging AGP system on its way down
the drain. So I'm curious about using the Nvidia 7800 series as an
HTPC.

I'm also interested in knowing how well the 7800 card would perform in
outputting an upscaled video to the TV screen. In the past, I've used
a ATI 9800 Pro to attempt upscaling a 720x480 DVD movie into higher
resolutions with all the bells and whistles (noise reduction, etc).
The framerates slowed to a craaaawl. I've always suspected that this
was largely a CPU bottleneck issue, not a video card issue. Would the
7800 GS video card improve performance in this area at all? And how
well would that video card be able to record TV programs in HDTV
format?

There are also three flavors of the 7800 GS available: the vanilla 7800
GS, the 7800 OC, and the 7800 OC Superclock. Obviously, the Superclock
would yield the best game performance of the three. But would the
extra heat and supersized fan be a problem later on?