Okay, I just replaced all my networking components in all my machines this week. I have three desktops 2 have Rosewill 802.11 b/g/n Wireless LAN PCIe card rated up to 300Mbps, one desktop with a Edimax USB wireless 802.11 b/g/n 150 Mbps, and a new Dlink DIR-615 route rated at 300 Mbps. So why is my transfer rate only 30 Mbps?
No one actually gets the rated speed w/ wireless, so 300Mbps is never going to happen. Under ideal conditions, you might get perhaps a 1/3 of the spec, so we're down to 100Mbps (but let's be generous and say 120Mbps is possible). One of your clients is using a single-stream wireless adapter (150Mbps), so 120Mbps is not going to happen either. Under ideal conditions, actual results w/ a wireless adapter rated at 150Mbps is perhaps 50Mbps. Here again, we'll be generous and make that 60Mbps. Finally, whenever two wireless stations are competing for the same frequency, all other stations must WAIT. In this case, each wireless client is competing for exclusive access to the wireless router. The net result is that the effective bandwidth between the wireless clients is roughly halved, or about 30Mbps. And add even more wireless clients accessing that same router at the same time, and it can get even worse.
And that is how your brand spankin' new 300Mbps rated router can find itself running at a paltry 30Mbps.
That's why I always say, wireless only offers one advantage; convenience. In all other respects, it sucks (speed, security, cost, complexity, you name it).
If you want some improvement, upgrade the Edimax to a dual-stream wireless adapter (300Mbps).