If your ISP can send multiple IPs through the circuit and you get a cheap switch, then you'd pull IPs in parallel by static assignment, keep in mind there is no firewall and your IPs are 100% public with this option. If you turn off DHCP and NAT, then you should be able to use that ADSL modem/router as the switch for this scenario.
If your ISP is only sending you one IP and you can't get more than you must use DHCP/NAT, hence you must use a router.
I'm getting roughly 116 Mbps down
This would imply that this is a local gigabit connection between the cable modem and PC.
The WRT160N only has 10/100 Ethernet ports, whereas the Cisco modem does have a gigabit port.
You would need to upgrade to a router with gigabit WAN & LAN ports in order to preserve this downstream rate.
Here's a chart indicating the range of WAN-to-LAN-port performance among various routers. If the measurements are accurate, then even "gigabit" ports are not a guarantee for fast throughput.
ADDENDUM
Because how else could they advertise 300 Mbps wireless speed? Thinking about it again now, I suppose it could be shady advertising with the 300 being for ad hoc network purposes only.
That's not shady advertising at all.
The wireless link is fully buffered from the wired links, so the wireless speed is completely independent of any wired link speed. Each link can transmit & receive at its full speed without regard to the speed of any other link.
Almost all low-cost Ethernet switches employ the store-and-forward (rather than cut-through) method, which also means that each Ethernet frame has to be completely received before transmission can commence to the destination. Routers and switched are computers that have local RAM to buffer/store the Ethernet frames as they are received.
The widespread "weakest link in the chain" analogy applied to throughput is often misinterpreted as if all links get slowed down to the speed of the slowest link of the communication path.
That is not a correct view of the data transfer.
Digital data is almost always transferred in packets or datagrams or frames (rather than streamed as continuous bytes) and these packets/datagrams/frames are almost always fully buffered when received and then forwarded.
So there is no dependency of the speed on one link with another link.
A low average throughput number does not mean that a high-speed link was actually slowed-down by another link in the path.
It's the dead or idle time of the transmission links (and the the processing time spent by the router or switch) that gets averaged into the total time to transmit that causes a lower average throughput number.
Best Answer
100 megabits per second can easily handle a 24 megabits per second down stream. The biggest reason to go gigabit is for communicating on your local network. If you want to transfer a movie from one computer to another, gigabit should be 10 times faster (network overhead and packet loss means it's not actually 10x, but close).