I still have the duke in mine, but it has the indy transmission (manual) which is geared taller so it is plenty fun at city speeds. Top speed suffers though so it is not a long distance driver. I don't do much highway driving so it works out. I've looked at doing a swap, but the current setup works fine and there is cost and down time involved.
The duke also has decent room around it to do repairs which is a pro. Like Dan says, in the end it's up to you. It would definitely be an easier decision if the duke breaks though.