I am developing a soil erosion model in QT (mostly the interface is Qt, the model itself uses some Qt but is mostly plain C or C++), http://sourceforge.net/projects/lisem/. Now a user asks if the application is faster on a 64bit machine. This type of models typically simulate the water balance for gridded maps of 500x500 cells and use some 400 steps to do that. So its really number crunching.
I have no idea, if 64bit is faster, I can't test it. Should I do a certain way of compiling?

thanks