I've got a 400Mbps internet plan, and I usually hover at around 350mbps through wifi. Yesterday, my download speed suddenly slowed to 10Mbps even thought I didn't install any programs or do anything else of the sort. My upload speeds are still fine at 100Mbps (which they always were and this doesn't bother me). As for location, my tower is not that close to my router, but even after moving it directly next to the router, it speeds up only marginally (+15Mbps down, +50Mbps up). My laptop still runs at 300Mbps down and 100Mbps Up in the spot my tower was.
I've rebooted literally everything and updated every driver under the sun.
At this point I might do a fresh install of windows, but I'd rather not if there's another option.