300Mb is actually 150/150. It's doesn't run "full duplex" (I think that term is incorrect for wireless but the idea is the same). Also that is at full signal strength and more often then not you have other networks nearby that add interference. The only time I've seen the full speed kick in is on my 5ghz wireless (no other 5ghz networks are around me,) with my laptop practically in line of sight of the router (within 25ft). I suspect the router can't handle full wide 40mhz channel speeds, and even if it did, you're not losing much due to overhead.