It ships with (an old version of) OpenWRT preinstalled. It doesn't get better/friendlier than that
Add a nice case (for instance from netgate.com - they have them but the page for that product seems to be broken right now, sigh) and powersupply (48V DC, netgate has them too).
Finally, add up to three minipci wifi cards (and make sure to get pigtails and antennas). A good vendor for that stuff is pcengines.ch; the Wistron DNMA92 Atheros 802.11a/b/g/n card is cheap at $26 and it uses the ath9k driver (no binary blobs). PCengines also has cheap pigtails and antennas.
All in all this costs quite a bit more than your run of the mill access point, but this puppy is a lot more powerful than your average access point.
We're at almost 200K tickets. RT scales fine, you just have to tune it a bit. And run it on PostgreSQL, and *definitely* tweak your PostgreSQL for performance.
In older versions, many indexes were missing by default. That may have been fixed more recently. Also, PostgreSQL 8.3 made a huge difference for us performance wise.
Computers are not intelligent. They only think they are.