Hello,
After struggling more than a day on the latency issue with AC7260, it looks like i found the cause in my machine (Lenovo Y50). Right now I'm using the latest driver from Intel Download Center (17.1.0.19) with small changes: Ad Hoc QoS Mode (WMM) - Disabled, U-APSD - Disabled (but this should not mater). Running Windows7 found that when the adapter is scanning for networks it then creates additional latency (up to ~2600 ms) and then goes back to normal (~ 1 ms) reported when pinging to the AP (D-Link 850L).
So what i did - disabled the background network scans when I'm already connected to the AP. Found this article useful explaining the issue: How To Disable WLAN Background Scans - gHacks Tech News and finally the "WLAN Optimizer" program solved my problems! http://www.martin-majowski.de/wlanoptimizer/
Hope it helps the others having the same issue.
Cheers,
Ilian