Vista Wireless Performance Questionnaire

My Wireless problems are fixed when I change Readynas Duo to 1492 but then my wired gigabit clients slow down by an average of 50% Is this normal?

1) Has MTU been changed to 1492 and running Windows Vista SP1
Yes

2) Model of Wireless Router and Firmware used.
D-Link DGL-4300 FW. 1.9 (latest) also tested with 1.7 (no difference)

3) Wireless Card Model and Firmware
Intel Wifi 5100 AGN driver 12.1.0.14

4) Connection Speed that you are seeing for Wireless Adapter. (54Mbps/24Mbps)
54 Mbps

5) Connection Speed between ReadyNAS to Router (10/100/1000Mbps)
1000Mbps

6) Throughput from Windows XP to ReadyNAS and Vista to ReadyNAS. Both Machines at or near same location. (Read/Write MB/sec)
XP up and download 2.5MiB/sec
Vista up and download freezes or averages around 10Kib/sec When I change to MTU 1942 Everything fine and 2.5MiB/sec

7) Throughput from Windows XP to Vista (Read/Write MB/sec)
From wired XP to wireless Vista up and download 2.5MiB/sec

Wired XP and Vista performance drops from 25MiB/sec download to 11MiB/sec when I change MTU to 1942
Don't want to suffer freezes and slow transfer rates on my Vista wireless but also need the full speed to my wired installation.

If you need more information to solve this I always want to do more testing...
Kind regards

Jellen

UPDATE: Also forgot to mention that I connected my Readynas to Vista and XP machine and still got a max read speed of 11MiB/sec when I change MTU to 1492, tried with other utp cable too