Ah no, you are going the extremes.
Example, I notice my 1080 video stream takes ~12 mbit, my 802.11G tops off at 27 mbit, and yet I get the occasional stutter. It's not necessarily total bandwidth, but without QOS, you have to assume the router precesses traffic in a round-robin fashion(?). So OK if I am the ONLY user at all times, and there is no interference by neighbors, or microwave fine, but in real life...
In a perfect world, we'll be all WIRED but people want wireless, where there are more variables involved.
Ahh... i see. you're wanting QoS on the Wifi (sorry when you said "lan" i presumed wired).
Still, the Airport Extreme does up to 300 megabit over 5ghz N, and i generally get at least 100 megabit anywhere in the house. So in that case, QoS not needed...
But i see your issue.
Yes, without QoS, the router will process traffic FIFO (first in first out).
Still, QoS can only be applied outbound from the device. So again - if you're throwing 30 megabit at it from your PC, the wifi on the router is going to need to handle it (it has already been sent, and can't discard what is already in flight - even if it drops the traffic on arrival, it took bandwdith to get to the router), and it will consume Wifi bandwidth, irrespective of what QoS settings you have on the router. Unless your end device is ALSO doing QoS marking and bandwidth management (i.e., rate limiting what it sends) on the traffic as it leaves the originating device (PC, NAS, whatever).
Also, as Wifi bandwidth is shared between all devices - all of them will need to be doing QoS marking for it to work effectively.
QoS is not a magic bullet. Also, it will only help by discarding traffic - the stutter you are currently getting, i suspect won't get any better if data is dropped and a re-transmit is requested (if it is carried over TCP, if it is UDP, it will just get discarded and you'll perhaps drop a frame or glitch? depending on how you're streaming the data)... at some point, you simply need more bandwidth.
I suspect if you just upgrade to an N capable access point/wifi adapter, your problem will go away without needing QoS. And I don't believe that QoS is going to help your situation much even if you were to attempt to do it over wifi.
QoS is most effective when you have an incoming data stream that needs to be shaped to fit a smaller pipe on its way through your router. e.g., if you were trying to determine how to shape your 30 megabit wifi down to 1 megabit outgoing ADSL. You simply prioritize what you don't want to drop...