I am still currently on 2.2.5, however, I have been testing the later versions every once in a blue moon but always put it on the back burner due to the many bugs. I pretty much gave up on the Store Import and have decided that when the latest version is stable enough, I will make the store look like I want and then manually import my database.
I decided to go ahead and check out 4.3.3 when it came out. It's a basic install with demo data. I created a new theme and have gotten about 75% of the look and feel done. Today I got the notification of the upgrade so I went ahead and tried it. It seems that CSC has put a lot of time and thought in the upgrade process. The 4.3.3SP1 was quick and painless so not too much to comment there. The 4.3.4 upgrade went smoothly as well. I was impressed with the upgrade warnings of what to do and especially the PHP script timout check. The entire process took no longer than 30 minutes. Is disabling 3rd party addons really that necessary? That might not make some happy if they have a bunch of 3rd party addons. The only thing I didn't like was the fact that there were no file comparisons of the local changes that were made. I only had about 5 and when I went to check the files that were modified, I only had an option of setting it to resolved or not.
Anyway, I am still checking other things (currently comparing the upgrade to a fresh 4.3.4). I'm not sure if everything went smoothly because it is a basic install with a tiny database compared to what it will be but I just wanted let everyone know how it went. I will report back if I find any issues not discovered yet.