The 270 Mbps is for the 5GHz channel. Theoretically, it's supposed to go up to 300 Mbps. My Alu MB gets 300 Mbps, but my MBP only gets 270 Mbps. This of course is affected by how far you are from the device, any interference, walls, etc.
If you're running a mixed b/g/n 2.4 GHz network, your max speed will be ~170 Mbps. If you're running only a b/g network, it will be 54 Mbps. If you're connected to the mixed network and a b/g device connects, speeds will be slowed down while that connection is active.
I'm not sure how the dual band works on the new base stations, but if they create unique SSIDs, you'd have to be connected to the 2.4 GHz network SSID to be able to test its speeds. Otherwise you'd need to test it from an N enabled device that can only connect to 2.4 GHz networks, or temporarily disable your 5 GHz network, though the speeds I mentioned are most likely what you'll get.
