I don't have enough experience to suggest what could be wrong, however for a different genre of connection for redundancy what about Satellite?

See: http://www.hughesnet.com/small-business.cfm

Regards, Neal

Have you tried tweaking the load balance policy and split the traffic out. So send HTTP down one connection & then send HTTPS down the other... Are you using any other filters? Content filtering for example. Have seen that take down the performance a few notches. Doubt its anything to do with the circuits or the 120. Most likely config knots in the Draytek.

My issue is very similar

Both my WAN's are Fixed Business Static, WAN1 and WAN2 supply certain services ie WAN2 is web-server and email server , while WAN1 is Security camera's and VPN etc

All worked of firmware 3.3.3 ( 3rd November 2009 ) for WAN1 and WAN2 except i keep getting crashes 3 times a week ( router freezes and needs rebooting manually )

I tried once to upgrade to firmware 3.3.4 in june 2010 and i came into the problem that WAN1 over-rides WAN2 so there for no emails and no web-server so had to downgrade back to 3.3.3

However this week the Vigor2820 has been crashing 6 times a night now and needs manual rebooting ( router supplied internet for business hotel and guest network for hotel ) , so had to try upgrade to 3.3.4.1 , now that it doesn't crash but only can have WAN1 or WAN2 enable but not both

All draytek hardware are still in the 12 month warranty and may have to go back

Whats DSL service are they on? ADSL2+?

Both DSL are Manx Telecom Business Static 20:1 ratio ADSL2+ 16MB/s down stream 512KB/s upstream each

"UPDATE" - thought the crashing issue would be resolved with the latest 3.3.4.1 firmware from my semi trusted firmware that allowed dual WAN 3.3.3 , So may have to either downgrade back to 3.3.3 to resolve the Dual WAN issue but still have the crashing 6 times a week

The router is still in its 12 month warranty till december 2010 , would i be better getting a swop out or upgrade to a more professional dual wan business type router

You could use a Cisco 1841 with 2x WIC1ADSL cards installed. Quoted thoughput is only 40Mb/s though. Although I have done a basic config on an 1841 and happily pushed through 80Mb/s in a lab test.