I have just recently started to do the same thing that zimzamzoom mentioned, however I have no logs with concrete evidence that getting the extra tick on NT is worth it or not. Obviously, simcraft continuously is putting it as a dps increase given the action list I have described (which is similar to the scorch weaving method that most mages are using at this point). To note, Frost armor in general seems to be a dps increase according to simcraft. As I said though, I have no logs to back this up. However, I do have this;
http://dl.dropbox.com/u/76387164/495...%20Scaling.png
This is a scaling of the next 2500 points for my personal character on a "helterskelter" fight - 495 mage with 4 pc. I expect most people will be the same. I think we can safely say that at this point, there is no obvious Mastery>Haste benefit and if either of them DO benefit over the other it will be a matter of playstyle and fight mechanics.
Also, the one caveat to swapping to frost armor is that I swap back to Mage Armor when using Living Bomb since the haste required to get an extra living bomb tick is simply out of reach at this point.