[mythtv-users] Frontend vs. backend: Which one needs to be faster?

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I'm going to be upgrading my Myth box very soon.  But I was hoping to
keep my old, tired, slow PIII 866mhz as either my frontend or backend.
 Due to video issues, it will probably have to be the backend.

The question I have is which box needs to be faster?  Hopefully the
answer will be frontend ... ?

Thanks in advance for any opinions!

TLD