I recently got a Cosmos and Vive Wireless and I would like to chime in.
Not all PCI-E lanes are the same. Some of them are directly connected with the CPU (Good for Wireless) and some are handled by the Chipset (Bad for Wireless).
I'm using an i7-3770 (clocked to 4.3ghz on all four cores) and an Asus Maximus V Formula motherboard (Yes.. it is a potatoe on paper but it works well enough with my 1080 Ti). The first two pci-e slots are directly connect to the CPU and I haven't had too many pixelation events when using the Wireless card on those slots.
However, if put the wireless card on the other spots, I get constant pixelations, likely due to added latency.
Right now I'm testing which processes (vrserver.exe, vrcompositer.exe, vivevrserver.exe, vivevrcompositer.exe) I can switch to high priority with Process Lasso as I'm getting some pixelations in demanding games. I want to squeeze as much from my 3770 + 1080Ti system.
So yeah, all tips and tricks are welcome.