Well I searched and didn't find a lot, so here's a question for Dave Atherton:
I have 300 hp 3126. The last time I had it at a CAT dealer they ran the serial number and told me it could be upgraded to 330 HP. Now I'm not all that thrilled about 10% more hp - but surprisingly, the torque curve for that engine mapping is really flat compared the the 300. So it seems from a drivability standpoint, it's a good idea.
What are the downsides?
Also, I've received a wide variety of prices when I've inquired of various dealers. Best price was $650, which for just plugging in a programmer and doing its thing, seems steep, but not compared to some of the other quotes I got.
I could see where at the purchase of the coach, there are warranty issues to consider, but after a significant period of time, should just be a labor charge for the most part.