I did just 2* and here is my write-up:
http://ecomodder.com/forum/showthrea...tml#post244353
What's the stock timing on your VX? Does it have a knock sensor? 2-4* shouldn't hurt anything, and it will help--very modestly--to produce more low end torque, which is useful for us hypermilers since we drive in the under 2000 rpm range most of the time.