The wifi performance on my I5 Surface Pro 3 is remains miserable after the update.
I use wifi mainly for file-sharing between my desktop and the Surface. To demonstrate the dreadful performance, I transfer a 1GB folder containing three files. Before the update this took 47 minutes 4 second. After the update it took 38 minutes 2 seconds. A great improvement you say?
My son had a small Patriot 11n USB adapter sitting around, so I disabled the Surface internal adapter, plugged in the Patriot dongle, and transferred the same folder. Before the update this took 1 minute 46 seconds, and after the update it took 1 minute 2 seconds. My wife's old Dell laptop does this transfer in about 2 minutes.
After the update, the Surface internal adapter gives me still 3.8 Mbps (says Task Manager) and 355 KBps (says the copy progress dialog). The Patriot dongle gives me 131 Mbps (Task Manager) and 17 MBps (copy dialog).
The Surface internal adapter is 36 times slower than a cheap dongle.
Something is really really wrong here. Note that the only thing that changed in the above tests is the wireless adapter on the Surface -- no other network changes.
I'm curious.. what router are you using?