|I've never come across, or have seen an ad for, a high speed cable combo router / modem. You probably need to get a standalone wireless N router, connect it to a standalone cable modem. |
I've never heard or or have seen an ad for an adapter that can be used with a combo DSL or ADSL router/modem that allows you to connect to a cable high speed connection. I very much doubt that they exist.
You don't benefit from a wireless N router unless both ends of the wireless connection are wireless N. They're backward compatible with wireless G or B, but if you connnect to a wireless G or B device, you have the same limitations that those older standards have.
The cheaper wireless N routers have 10/100 mbps wired ports.
The more expensive ones have 10/100/1000(Gigabit) mbps wired ports. If you don't need to connect between wired network devices at 1000mbps speeds (approaching but not reaching 100 megabytes per second rather than 10 megabytes per second; requires Cat 6 rated network cables), such as if you want to use that capability to transfer data between computers via a cross wired network cable, then the ones with the 10/100mbps wired ports are fine. Either will yield you the same max speeds on the internet.
Most people do not need a dual band Wireless N router, the most expensive kind.