I put considerable value on 42s over 38s. I won't even buy a 9760 or 9770 for resale purposes unless it has the 42s. To me it looks like the 38s get sent to auctions cuz they are hard to resell when you have machines with 42s on the yard. I noticed that at the last RB auction in Saskatoon. Lots of the Deere units had 38s.
Have also noticed the 42s perform better in soft conditions. Seems the larger diameter helps to stay on top.