S2S VPN

I'm not sure this belongs here, but I'm having some SSL site-2-site VPN issues with version 9. (Running on Vmware 4)
I have 2 VPN connections to an UTM.
The UTM that's being used for the server connections is still running version 9.000-8.
The server is behind an 6mbit down / 1mbit up ADSL line.

I have 2 clients connecting to it;
1 through an ADSL line, 12mbit down / 1mbit up and still running ASG V7 on physical hardware.
2nd connection is a cable connection, 120mbit down / 10mbit up running UTM 9.002-12 on physical hardware.

This works fine, no issues so far.

But as soon as I upgrade the UTM that handles the server connections to 9.001-18 or to 9.002-12 the issue starts. The VPN connection gets very very slow...
When I ping from 1 site to a server in the main office, normally I get a ping time around 35ms, after upgrading the UTM the pings go up to 350ms or higher, up to 850ms.
Even RDP sessions time out then....

When I revert the UTM to the snapshot I made before upgrading the problem is solved.

I haven't tried 9.003 yet, but I don't see any changes to the site-2-site VPN part, so I don't really think that will help much...

I hope this description is clear enough to "draw" a picture of the situation and I hope somebody can help me solve this.
Thank you very much!
Regards,
Erwin.