Right. Managed to free up some time to thoroughly research this problem for myself. After a good 30 minutes mix-matching settings in Device Manager to no avail, I ended up in the BIOS of the NUC (a D54250).
In the Power tab, I was tinkering around with the ASPM and ACPI tick boxes. Initially, these were left unticked. I ticked both, saved the settings, and booted into Windows (7 x64).
Windows wouldn't initially connect to the internet. Going into Device Manager, my 7260AC card was now classed as #2, and all the wireless settings had been reset. Okay, maybe the PCI setting changes affected how the system refers to the 7260 card. I ran the windows troubleshooter and it reset various IP settings, and I was finally on the net.
It's now fast. At times.
To check the connection reliability I started up cmd and pinged my router. The pings are epic large (averaging around 750ms). But the internet speeds are still very fast most of the time.
Now, I went back into the BIOS and unticked both boxes and rebooted into Windows. The Device Manager now shows the original 7260 device (without the #2 branding), and my old wireless settings are now there. Going onto the internet, I'm greeted by the dismally slow speeds once again (can't stream a 1080 Youtube video without it buffering every 2 minutes). But the kicker is that running cmd and pinging my router again, the pings are averaging 200ms and less.
The cmd results are somewhat contradictory. And I'm thinking that this whole issue could potentially be related to how it is powered by the host machine. Heck, the wake-from-sleep fiasco is probably classed as a power-related issue, so the throughput / speed variances could very well be due to the same class of problem(s).
For now, I'm going to continue tinkering with the ASPM and ACPI settings. I just want a fast (and reliable) connection. My Asus USB dongle takes up a USB port and was never intended to run 10 hours a day.
I know the mods here are taking quite a bit of flak for the sheer stupidity that the Intel wireless engineering staff have apparently shown us forum dwellers. I'd suggest get your acts together and get this resolved. I've had a look through the Lenovo and the now unmonitored Sony Vaio forums and the 7260 class cards and their owners are literally at the end of their patience levels. I don't live in the States, I can smell a class-action suit or two coming quite soon by some (very) wealthy Vaio Pro 13 owners...