Pre 1.6 I had no problems with the framerate, when 1.6 dropped I now get random slowdowns that cause the game to drop to less than 1 frame per second.

If you manage to enter VATS or open your pipboy the framerate returns to normal. If you leave the pipboy or VATS, or browse to the world map page of the pipboy, the frame rate grinds to a halt again.

Loading a save doesn't fix the problem and often causes an infinite load or crash. The only fix is to restart the game. Thankfully you can press start and save, though the process can take several minutes due to the slowdown.

I'm hesitant to say that this is preferable to the now absent freezing, because it happens far more frequently than the freezing did, especially as your save grows.

Sort it out, please.