Just to add
the 2925 its firewall is up to 200mbps
see specs
http://www.draytek.co.uk/products/business/vigor-2925

Performance:
Firewall: Up to 200Mb/s
IPSec VPN: Up to 50Mb/s

You may want the 2130n which has 500mbps / 800 claiming at Taiwan page
http://www.draytek.co.uk/products/legacy/vigor-2130n

Up to 500Mb/s WAN Throughput - ideal for fibre services

Up to 800Mbps WAN throughput (ideal for FTTx services)

Is a bit old but has everything up to date (including firmware) and you will not have to worry if even VM go more than 200mbps speed

But i believe if you disable wan 1 & usb at the 2920 will go up to current VM speeds to keep you going for a while