Hi ,
as said from various users before changing the power mode of the adapter will bring back the speed:
Devise Manager, network adapters, Intel .. 7260, Advanced, U-APSD support= disabled
My experience is that the driver version 17.0.6.1 works for my N7260, but the newest 17.1.0 does NOT !!
Lenovo Y510P
N7260
Win 8.1
Intel i7-4700MQ