Not to encourage further sleepless nights among the multi player air combat community, but have you lot played Aces High? It's by far and away the mutt's nuts when talking about online furballs and looks bloody fantastic to boot. (and you get to drive tanks as well as fly spitfires and b-17's and so on and so forth).
<a href="http://www.hitechcreations.com/htchome.html" target="_blank">Aces High - just look at the screenshots!</a>
This one DOES have a subscription BUT you don't have to pay for the 8 player head to head option EVER so if that meets your needs it's completely free (and you get the usual free trial).
Try it, it rocks.