A router shouldn't case a problem, latency might go up but bandwidth should remain unaffected. Switches should be intelligent enough to know where the data is going as they are programmed for that, the "router" part just communicates in the IP whereas the switch talks in hex keys or mac addresses. Feel free to correct me on anything i may have gotten wrong but as far as what i know a router shouldn't be a problem, at least any routers made in the last 5 years. It is a well known fact that cable internet is very volatile in actual speed and depending on your ISP they may not add the necessary hardware when their services are being strained. Some like comcast will scan your usage and slow down your BT downloads to save themselves the money that would otherwise need to be invested into expanding bandwidth support for that area. From what I've heard from people in the business (the backbone side) is that the typical station will be designed to run at 70% before its deemed necessary to expand bandwidth to that area, so nobody ever reaches the cap. HOWEVER, preferred customers, such at ones purchasing extreme or otherwise like-named services operate at a lower tolerance and are ensured much more reliable speeds. My personal experience when switching from 10mbps to the standard 5 mbps my ISP provides (Shaw) is my actual bandwidth went from 9000+kbps to around 3000-3500 kbps, which lends to my theory quite nicely and shows that i lost considerably more than half of my bandwidth showing that it is not a linear drop, indicating that a separate system is used for us regular folk.
Things i recommend you try:
1. speedtest.com/speakeasy.com
2. try a different computer (a buddies perhaps) see if anything changes, be sure to try throughout the day as peak usage times will see a drop in bandwidth
3. talk to your isp about it...they DONT KNOW and WILL NOT act until they get complaints in that area, call them...ALOT
4. be persistent, refer to step 3 until it is resolved
5. at this point you should either cancel the service or save some cash and get the regular high speed as it is clear your isp is not willing to invest into your neighborhood to add the bandwidth