Well trying the public IP address to a connected network devices doesn't seem to work. Not sure what is going on.
Heres what I recommend:
1. Phone contact the ISP and ask them if they can help you bridge or get the public IP address from the ISP Modem to the router. If at all possible.
2. I see that this DSL modems is fairly old, 2006. I would ask the ISP if there is a newer more up to date DSL modem that they can give you, preferably one that can either be bridged fully, provide a Public IP address to the 655 or has a configurable DMZ option. The DMZ can be used for the 655 as a last resort.
If either one of these can be done and fully completed so that the 655 can be the main host router, then you should be good to go and be able to test speeds accurately.
Right now speeds will be inaccurate. I'm hoping that either one of the options will get you going. Your almost there. I'll check back when I get home and see how things are and go from there. You need to get to a single NAT condition here.
Sorry it didn't work out as I hoped.
Keep us posted.