Gotta love updated drivers. Did everything on here to get 300mbps and there was just no way I could get over 150. Servicing a laptop for a client, I realized that his had an AR5B91 and it ran at 300mbps on my network, so why wouldn't mine?
Took his older driver and put in on mine. Runs 300mbps now.
WPA2
AES
Driver is athr.sys (windows/system32/drivers)
Latest version I had was 7.7.0.396 (bad)
Older version that works: 7.6.0.126 (good)
Rename old driver, drop in new driver, reboot.
I'm running vista on this laptop. YMMV.