Since I turned into a bat driver (since Nov/2011 I've been played only at night) I started to tweak the game according to nighty trips, but only past week, and due to new core update (the game is running far better, at least to me), I surprisedly got a very nice (and quite unbelievable) smooth performance even within 10-14fps range in most of routes! (people playing over the 30fps barrier please don't laugh!).

Someone posted about the difference between
framerate (the time in miliseconds to render a frame) and
frames per second (how much rendered frames is loaded by second) and how the "shader" option effects the smoothness when playing (even at low fps) because it impacts the framerate more than the fps. I also have a medium rig, and what I'm doing with excelent improvements is setting the in-game options to High or Highest, and then (with Custom option) reducing to lower settings especially the Shader (don't confuse with Shadows) and others that don't make relevant difference at night: Water, Passenger, Distance View, Terrain texture etc.
In my country we have a say (in literal translation): Who doesn't have dog, hunts with cat. (likely, in English: one makes the best of a bad job).
Cheers,
Lisboa.
Who doesn't have dog, hunts with cat.