That is a problem I'm facing right now. I need to specify the hardware that will run my piece of software. The thing is: the project isn't finished yet, and I need it running in "real" conditions before I can go on, conditions which I cannot reproduce at home; what I can test at home barely scratches them. We don't have much money to spend (it's a research at college). Feels like a catch-22.
How can one get a good approximation of what setup is needed without having the means to simulate accurate work conditions?