One other point. I have noticed that if you are sitting too close to the wireless source the SP can become overwhelmed and fail to connect. For instance, at times I can connect to the wifi extender at the other end of my home but get "limited" connection from the one 5 feet away. This works sometimes and not others. Again, weird. If I pop in a usb wireless receiver no problems so it is apparently and issue with the built-in (which sucks). Hopefully a software issue which will become resolved eventually.
I know this may be a little late, but I too started to get very slow speeds on my SP 128 as well. I am thinking of trying the roll back on the Marvell driver too. But before I was going to do it, I thought I would try a high speed Cisco USB 300 first in the only usb slot we have and Bam....it started getting 68 to 69 megs DS and 5 US. I first tried using the Asus ea-66u 3 in 1 router in extender mode, set to 24 g, but it to was slow, then tried using my 5 g directly from the rt-ac66u Asus router in my home office, clean on the other side of the house and get great speeds. I am getting what I pay for 68 down stream, 5 up stream. But with only 1 usb port, kind of would like to use it for other accessories. I have not had much time today to really get into it, but I do like the roll back idea....I should have thought about that myself, but like many others...still trying to get a handle on his tablet. Been using iPad for a couple years now. Got this SP so I would not spend so much time n the office, now I can handle just about everything my desktop win 8 pro Asus X79 deluxe home built system. First thing I did was get remote access to my other systems I have in my office, being a disabled vet...this tablet helps me a lot, really looking forward to its development. I am a TechNet subscriber, so its nice to be able to learn, keep track of new software development as well. Learning myself to write apps in the future. I wish others would talk about the WiFi problems to, I have 2 years insurance so I need to see of I need to return it for another tablet or wait and see if this problem is fixed. Knowing that the usb WiFi gets the speed I once had when I got it home with it before the updates. I know it was the updates, but not sure which one until I read the earlier post. If the usb WiFi works then its got to be a driver out of whack, hardware issue, but not really thinking that's a problem because the usb WiFi works just fine, its just when I switch to internal WiFi, its so slow and intermittent.
Well maybe I will see others post soon. I going to try the roll back and report back to the group here with my situation.
Have a great evening guys!