jmcafee, thank you for coming back to revisit this thread. I installed Windows 10 on my T400 on 7/29, hoping that MS would have most of the kinks worked out by then. Instead, it has been the worst experience I have had with a Microsoft product..... EVER, and I will likely return to Windows 7 x64 Ultimate, as I did after installing Windows 8. I never bothered with 8.1 after that experience. I have 2 tested images of 7, so return will be a breeze if I decide to go that way. In fairness, I would like to see if I can get 10 fully functional before I do.
Following your suggestions, I am still having problems, some minor, some aggravating, and a couple of show stoppers.
Your tip on the OSD driver was very helpful. I had tried a few versions going backwards, with no success, but gave up before going all the way back to your suggested version. You must be a very tenacious fellow. However, I still do not have access to the brightness function, and as far as I have seen from other reports, no one else has had any luck with it. I use that feature a lot. The Win 10 feature needs an extra step, and once you have access to the function, it is pitiful by comparison. Did you actually get that feature to work?
The loss of the Switchable Graphics function on the fly is a big loss for me, since I used it a lot. Having to shut down, restart, go into the BIOS to make the change is not my idea of a smooth transition. That loss, it would seem is permanent. I have not tried the third party drivers, which have had some success, but also some instability and blue screen problems.
The biggest show stopper for me is WiFi. I found literally an abundance of hits on Google searches, for all manner of laptops, and desktops, and dozens of potential fixes, but like others that finally returned to Windows 7 and 8.1, none of them has resolved the issue. About every third or fouth time I boot this T400 up, I have no internet access. If I fiddle around enough, and reboot several times, then after wasting an hour or so (time that I don't have to spare), I will get a connection. If you are problem free in this area, and are getting better than 2.4 N, would you please post your Property settings. From day one, I never had a single issue with Windows 7 in this regard.
I had planned to, and did reject all manner of MS "Spyware", but since some of it is hardcoded, there is no way to block it all. In fact, the ONLY reason that still has me somewhat interested in seeing this through is Cortana. There too, MS wants access to your data, so if I can get some of the other problems sorted out, I will activate it, and see what can be limited in those terms. In another month I will be switching out my Windows smart phone for an iPhone 7, so I will have access to Siri, which by all accounts is superior at this point, and since my phone is ALWAYS at my side, for the most part, if I role back to 7, I will actually be gaining productivity with a fully functioning laptop that was running just about as smoothly as one could hope for, and doesn't have an interface with icons that look like they were created by a first year graphic arts student that was heavily into Windows 3.1 as a retro influence. God I miss Aero. Someone should have informed MS that computers with more than adequate resources to run Aero, have been around for quite some years now, and hey, at least leave the option open.