Server :: Send Traffic Down WAN Link Depending On Client IP Address Range?

I am running Debian Squeeze with the following basic services running:DNS
DHCP
Samba
Squid

The server is setup with three NICs: eth0 (WAN1), eth1 (WAN2), and eth2 (LAN).The server addresses clients with an IP range of 10.0.30.1 - 10.0.30.254. Some clients will be set with reservations so they fall into the 10.0.40.1 - 254 range.

What I want to do is have any outgoing external traffic coming from the first range (10.0.30.0) to use WAN link 1, and any outgoing external traffic coming from the second range (10.0.40.0) to use WAN link 2.

I have sort of got something working. I have created a bare minimum transparent squid3 setup on port 3128, and set the iptables as follows:

Code:
iptables -t nat -A PREROUTING -i eth2 -p tcp -m tcp --dport 80 -j DNAT --to-destination 10.0.0.1:3128
iptables -t nat -A PREROUTING -i eth0 -p tcp -m tcp --dport 80 -j REDIRECT --to-ports 3128
iptables -t nat -A PREROUTING -i eth1 -p tcp -m tcp --dport 80 -j REDIRECT --to-ports 3128

I can get internet access, however obviously it only goes through one WAN link. It also seems slower than it should be. I experimented with tcp_outgoing_address, but seemed to not be my friend.