Traffic Shaping

My network's WAN bandwidth is being pushed past it's limit, crippling essential network services.  Traffic shaping to the rescue!

There are two sites, each have a soekris box with VPN over IPsec.  Searching the forum has told me that outright priority of VPN cannot be accomplished.  However in my situation there is only one network that each box is tunneling to.

I plan on creating a rule - outbound wan traffic destined for the private network at the other site is assigned to the high priority queue.  If I do this at both locations things should be peachy again, right?  

Should that rule would not accomplish what i'm looking for, is there another way?

You can traffic shape VPN or IPSec.

In the traffic shaping rules, you notice GRE and AH protocols.

GRE = VPN
AH = IPSec