Hum... how about displaying a text saying "Only displaying active posts from the last X days. To view list of all threads
click here.
So people would always go through the default X numbers as set by the admin or by their user prefference (mainly default as most users never change options). So yes, you would still make the full table read at times, but only when someone clicks on the link... and this would be around 1% of the times, I assume.
How about that?
Mateo Byler
CruceDeCaminos.com