Spectrum is not the only ISP involved in connecting you to each site. There can be issues at or on the other side of a peering exchange that causes delayed/retransmitted packets, which can make it take longer to transfer a file.
It is important to note that their speed claims only cover transfers within their own network. If you are able to successfully test to your rated speeds across the internet at ALL, then it would appear they are in fact meeting that metric... at least locally (throughput will be limited by the weakest link in the route). Things can simply go bonkers once you go through an IXP and are placed on someone else's network... things sometimes out of Spectrum's sphere of influence, much less direct control.
For a sort of visual demonstration of how easily this can happen, identify the address of your endpoint connection. Run a tracert (or traceroute in some environments) to that address and take note of where you leave Spectrum, and just how many hops and different ISP's can come into play after that. You may find you are only on Spectrum's network for crossing your state and maybe one or two more out... then hop on two or more different ISP's for the remainder of the route.
For example, to get to Square-Eidos servers in Montreal, I take 4 Spectrum/TWC/RR hops getting through the Carolinas, then two more getting into Atlanta to hit an exchange point. Then I have seven hops on Cogentco networks to go north through DC, NY, etc. Into Montreal. THEN I spend a few more hops on ORMUCO lines until I actually enter Square Enix routers. The entire route is well over 15 hops long just getting to the game servers across networks managed by 4 other companies aside from the network I am in charge of myself.
If things slow down as you traverse a congested third or fourth party network like Level3/CenturyLink, ALTER.net/Verizon, Telia, ATT, XO.net, Zayo.net, or any one of hundreds or even thousands of other ISP's out there, that is an issue with THOSE networks. If you find troubled routes, identify the ISP's involved as well as the endpoint address and report them to Spectrum... at the very least, report the endpoint. The more detail you can offer the better though. Tier3 needs reliable and potentially actionable data in order to even begin looking at such issues, let alone try to escalate the matter to see if adjustments can be made to the peering/routing arrangements to see if those issues can be avoided or possibly even addressed directly with any specfifc peer.
In my case,
I own my own router.. It's about a 2014 model from Netgear. A firmware update stopped all the disconnects and it is now rock solid no lags at all. But because of its age, only pulls in about 50mbs on the download.
When I upgraded to Spectrum from legacy TWC, I was getting the same speed. The modem I have is an Internet/Telephone combo and works great. This is from Spectrum. Since, I only download small files, my choices are to spend $60-$70 for a new router for the new speeds. Totally not needed considering that the reliability of my old router works great, and I don't want to rent a rent a Wireless router from Spectrum for $10 a month. Considering what I download, I don't need the extra speeds. In fact, if you are not a power user who is downloading large files, or you don't have a ton of people on your wireless network, you can get by with 50/5mps.
The OP would need a modem with Doc Sis 3.0 to 3.1 functionality AND a modem that supports gigabyte ports to get Spectrum's 200mbs speeds. Docs Sis 3.0 modems with a modern router go up to 330mps. If you get an additional optional faster Internet from Spectrum and want gigabyte speed, you must have a router that supports this and a DocSis 3.1 modem,