The modems for Cable (DOCSIS 3.0) can deliver 2-3X that speed, no problem. But modem/router combos will depend upon the CPU horsepower in the router. I imagine that most newer gigabit routers can handle 100mbit/sec with NAT, and I especially expect that a combo Cable modem/router can handle it.

Edit: The two cable modems I have here are each capable of 340-440 mbits/sec downstream performance (plus 120mbits/sec upstream), but neither has a built-in router. It's the router part that tends to be a choke point, because of the software (CPU) intervention required per-packet.

Cheers