If i were going looking on ebay id get a cheaper one like mine which i think is an SB61G2, for the untangle box, and one of the better Socket AM2 or Intel Core2 capable ones for a server.
But, there are many great Mini-ITX boards out now that can take advantage of a wide variety of CPU's. and that further extends the posabilities.
I've been seriously considering scrapping my M-AXT server build in favor of a Mini-ITX form factor. Space is at somewhat of a premium and while i'd love to be able to drop $1000 on a Mac Mini server, I just can't afford it. So i'm forced to scrounge ebay and my used parts bin to see what i can come up with.
Yes that would be exactly my situation, and what i might end up doing