I like syn oil, especially in winter, but diesels get oil dirty so fast I prefer to change it often and it's just too expensive for me to do that with syn. I also run veg and like to change oil often for this reason alone.
I may run syn in the samurai once the motor is broken in since I don't put alot of miles on it (but the miles I do are very hard), but in my Benz that see's 700 miles/wk, I could not justify spending the money, I prefer to change it every 3K and that thing holds 8qts. I use Rotella, get it at TSC in 5 gal pails, comes out to $9 and change per/gal.