FVS318N WAN to LAN low throughput

Hi,

I'm struggling with WAN to LAN throughput on our FVS318N. It's a fibre to the cabinet PPPoE service rated at 76Mbps download and 19 Mbps upload. When initiating a PPPoE session direct into the back of the 'modem' we see 76M on a mulit-threaded download test, however plug the FVS318N in and this reduces to circa 55M, then plug in our GS108P and JGS524 and this drops to about 40M. We are running the latest firmware version 4.3.5-3.

I have done a factory resest and just configured the FVS318N with the broadand settings with only one desktop client plugged in directly (no other switches or network components) and we still only get 55M. The FVS318N is rate at 250M WAN to LAN throughput so not sure what is going on here. Any help appreciated.

Thanks.