I now know:
GS-13 step 1 ART (Major) pay is 600-800 dollars less a month than an AD major with 12 years in (take home). You pay more in taxes and have to pay for your own health insurance. This of course depends on your AFTP allocation (how you do it) and AT days (minimum 15 days a year). Some months are better than AD, but most are an average of what I stated above. Step 3 and 4 start making all the difference in the world, by step 10 your are paid like an AD LtCol on the bonus until you are 55 (if they let you stay). Switching between AGR and ART is where it's at but that's a discussion for the bar. Oh yeah, alert makes a big difference as well.