Back to the OP: obviously the use of a C or D turbo is personal choice, and different folks fall on different sides of the line. Because of that there is generally pretty good opportunity to swap if you don't have the one you want. I had a C and swapped it for a D with another member. We both paid our own shipping and ended up with what we wanted for nominal cost. I wanted the additional power the D spins up (noticeable at higher RPM's but alone probably not enough to make it worth it to do the swap) and I didn't particularly care for the whine of the C.
The parts are perfectly interchangeable, pull one out, put in the other. While you're in there I recommend installing a pyro and cleaning stuff up.