Hi Andy ...
You wanted a "geek" reply , so here it is :
18 GByte x 8 = 144 Gbits
144 Gbits x 1024 = 147456 Mbits you have to move.
Your router has a MAX of 54 Mbits/second , but the overhead on encrypted WLAN is said to be up to 50 %!
So you actually have ,lets say 30 Mbits - if everything works 100%.
So (147456 Mbits) / (30 Mbits/s) = 4915 seconds or 1,3 hours would be your actual MAX performance...
You have 3,5 hours so this is actually poor performance (less than half of the possible speed).
Now , if I look at my setup (which is like yours) I see the following things which make MY connection slower:
- automatic adaption of the speed , including new training (maybe because of the "G+" standard)
- I have never seen 54 Mbit/s , not even at a distance of a couple of feet - normally I have about 25 Mbit/s
And THAT would translate to your measured performance !
My advice: use a cable an 100 Mbit/s ethernet for such transfers