I've got pfSense[1] running on a passively cooled embedded board[2]. I then use whatever wireless APs I want in bridge mode.
I like this because x86 will always be compatible with anything I might run in the future, and changing out wireless hardware from 2.4 N to dual-band N to ac has been trivial and required no thought to compatibility.
[1] http://www.pfsense.org/
[2] http://www.jetwaycomputer.com/ITX-JBC362F36.html