Desktop wireless slower than laptop wireless

[kakistos153]

So i was using a USB wireless adapter on my desktop for the last year. I recently upgraded my internet connection to 30Mb/s and replaced our trusty old wrt54g with the asus rt-n53 for wireless N support. Much to my chagrin I was still only getting around 20Mb/s according to speedtest.net. so i figured my wireless g usb adapter was to blame. I bought the asus pce-n15 wireless adapter expecting a 30% increase in speed which never came. It still runs around 20Mb/s. Same computer, 2 different adapters, the USB adapter had an extension cable and was positioned over the monitor, a good distance from the tower. The new adapter has 2 antennas on it.

The laptops in the house run around 28-32Mb/s.

The only particularly common factor is the desktop itself but i cant fathom why two different adapters which should both be adequate (i think) would be throttled at the same speed. they are both apparently very similar realtek chipsets but that shouldn't be super relevant either. anyways. any help would be greatly appreciated.
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Extra info, i'm sure much of it isn't useful but ya never know i guess.

Laptop: SATELLITE C650D-11E

Router: ASUS RT-N53

Desktop: Biostar TA970
Power supply: CORSAIR CXM series CX600M 600W
PCI Wireless adapter: ASUS PCE-N15
OS: Windows 7 Professional

ISP: Time warner, Cable
Connected devices: usually around 5

 

[Paul NZ]

The RT-N53 is N600 the Asus pce-n15 is only N300. So you'll only be getting N300 speeds not what the router can go to

The router will "step down" to the PCE-N15's speed. It would have been better if both were N600

Or dual band

 

[kakistos153]

The RT-N53 is N600 the Asus pce-n15 is only N300. So you'll only be getting N300 speeds not what the router can go to

The router will "step down" to the PCE-N15's speed. It would have been better if both were N600

Or dual band

Even still. they should be getting more than 20Mb/s. we're not talking MB here like. I'm pretty sure my laptop is only wireless g even, and certainly isn't dual band.