This is my setup, which is very similar to you.
ethernet 1 = VOIP = 10mb
ethernet 2 = all other traffic = 50mb
The problems I faced with this on my network was capturing all the sip traffic (as we have many devices that all use different standards, rules, etc) - this issue was overcome.
The next problem and still the one which gives me problems, is the routing of VOIP (in and out) this is very very important. Even with marking of packets, ports, IP's (to sip and PBX), connection types - this still has issues.
Also we have QoS running which made things more complicated.
My device would be to actually get a good consultant to setup the router for you and provide support for 3-6 months afterwards because there will be bugs and changes needed.
Also plan exactly what traffic you want to capture (video/voice/g729,722,etc) - this will be needed so you know or the consultant knows what traffic you want to send down each line.