That behavior of 7260 series card regardless of variants (7260N or 7260AC and regardless of laptop brand / model) has already been posted many times here. No matter what tinkering you do with the card or the proset, or power management, you can never eliminate that issue. That issue really sucks when you're uploading a large file then you have to start over again. You just have to wait for a fix in the next Intel update. No drivers have fixed this issue yet.
I also have a laptop with the 7260N OEM card. Here's my tips to at least lessen the occurrence of the speed drops to 2 - 11 Mbps:
1) Use Inssider to get the best channel for your router
2) Follow Lenovo's temporary fix here: Wireless / WIFI network disconnect frequently
3) Disable USB selective suspend in the advanced power options (Bluetooth uses USB interface) and it helps eliminate Bluetooth disconnect issue
4) Disable PCI Express Link State Power Management
With this temporary workaround, the frequency of the occurrence of the speed drop that never goes back to normal without resetting the adapter will be around twice a week to once per 2 weeks.
For those who have the 7260AC, their permanent fix to eliminate this speed drop problem is to connect to 5 GHz WiFi AC router.