at the company where I work we have a few D9R's which have the 3408 motors and the D9T that I was running last week has a inline 6 motor now I think the C16 motor can't remember for sure. I know the T's are quiker than the R's were and the T's also have all electronic controls for the blade and rippers and one D9T we have has full automatic gps control hit a switch and steer pretty cool system it will get you within .500 of an inch with your grade .
Engine change from 3408 (R) to C18 ACERT (T).