Hi simonq156,
Network transfers between PC and NAS were very up and down, they had a heart beat monitor type appearance, I get between 50mbps and 0mbps transfer but PC to PC across the network I was getting 105mbps+. I used a little program called netmeter which actually shows me the transfer rate, a little different to the method your using regards network utilisation.
As regards the connection of your router into the GS605 its dead simple, yes you just connect em up via a patch lead, CAT5e will suffice as your router is only 100mbps the switch is autouplink sensing so you don't need to enable any specific ports as the uplink. Then connect all your gigabit pc's into the GS605 and away you go.
I have a print server (Netgear again) connected into my router and also my XBOX will go into it as they only have 100mbps ports. My HTPC, office PC and NASbox all connect into the switch, I also have a wall socket in the spare room where I do a bit of system building connected up so I can access the network for installing any software I have backed up on my NAS.
The XBOX 360 does look very swish but I'll stick with my HTPC and chuck the XBOX into the conservatory and use it as a media serving for playing MP3's in the garden when the summer comes and the BBQ can be brought back out of hibernation
wilbur