If you guys aren't, you should really be using a site like this:
Custom rims, wheel tire packages for your ride - RIMSnTIRES.com
For the left hand column, put in the stock wheel and tire size. For the right hand column, put in the wheel size you're testing or expecting to fit. Play around with the tire size to get something close to stock diameter. It even tells you how the tire size and wheel width/offset affects fitment and speedometer readings and other cool stuff.
It's a quick and simple tool but super effective in helping you choose your next setup.
Other than that, nailing the perfect fitment comes down to setting your ride height where you want it, setting your camber to where you want it, and then fine tuning everything with some spacers. Use a ruler to measure how much outer clearance you have to figure out what offset wheels to go with.