QoS over VPN links for VoIP

I have 5 offices now with Cisco Call Manager Express systems running Cable or DSL lines for internet, with one of them on a T1 for internet. In 2 locations I have Cisco 1720 routers at the edge handling the internet connection, in 3 others I have PIX 501's. The 1720's can do QoS, but the PIX501 cannot (until a 7.x release comes out that might add that feature).

The Call Manager Express routers are either 2561XM's oir 2821's. QoS is setup on these devices as described in the CME docuemtnation.

Currently we just use VoIP on the local LAN, nothing over the internet on our VPN's. I want to experiment with some VoIP over our VPN links. I will setup some VPN tunnels between offices for this testing. A few questions:

1) Does the QoS setup on the CME router provide any benefit on calls once they are forwarded out over a VPN to a remote site? 2) Would setting up QoS on the 1720 edge routers (and the PIX's if added in the future) provide any usable QoS, or is the CME's QoS all I need? 3) What would be the proper way to setup QoS on the 1720's 4) Has anyone done any VoIP over VPN links on standard Cable/DSL lines (not vonage, but stuff they run themselves) Our service is all 3.0/384k on these lines and we use g711ulaw. How is the quality?
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