I've been browsing these forums and have found similar issues to mine yet no actual fix so I have hoping to gain some insight or a solution!
I recently bought a new desktop from Newegg - HERE . After some hitches of Windows 8's Search Charm crashing upon an actual search, I refreshed the OS and it solved that problem. Even before then, I installed a ASUS PCNE 15 wireless adapter. For whatever reason, wired to the router or wireless, I am getting wildly inconsistent download speeds. Speedtests show I am getting 36Megabits per second, yet my downloads from places such as Cnet are reaching only 100 kilobytes per second and Standard Def Youtube videos have trouble streaming well(HD Stream is very hit or miss). I downloaded Illustrator and InDesign trials from Adobe directly and those downloads reach between 2megabytes to 4megabytes per second.
Now, I have hardwired the desktop directly into the modem and speeds ARE consistent - CNet got the 4MB per second. I thought my router may have been the issue, it is a DLINK DIR 651, so I went out and purchase a Netgear N300. Same exact problem on the deskstop - download speeds barely reach 100kbps.
I have tried reinstalling drivers(though I am unsure of how reliable Windows 8's Device Manager may be for getting drivers), "flushing DNS", setting up Static IPs, disabling/re-enabling adapters, etc and I am at a loss for what to do next.
My laptop I have had for four years is perfectly fine, it downloads as it has been. I am not seeing what the issue might be as I've messed with anything I could think of between the desktop and the router.