I just registered here to post this thread because I've read so many different threads regarding this issue. I've spent entirely too much time trying to resolve this.
After fooling with processes, services, component drivers, etc., it seems everybody is in the same boat. What I did was boot the system in Safe Mode with Networking to test DPC latency. Unfortunately I couldn't run the DPC Latency tool in Safe Mode, but I could clearly see there was absolutely no problem transferring a 1GB file over my wireless network. Normally I connect at a maximum of 300Mbps and transfer files no faster than 9MBs with severe latency. In Safe Mode I connected at 450Mbps and transferred at 18MBs with absolutely no latency.
I tried for over an hour to disable processes and services in Windows normal operating mode to simulate Safe Mode. This didn't work, and I never figured out what's causing the extreme latency. Has anybody else had this experience with Safe Mode? It's driving me insane, and now I can't stream video with crackling audio. I've already tried replacing the wireless card in two different machines having the same problem. It's definitely a software related issue.