Generally I'm of the opinion that things like bike geometry and setup should be determined by what kind of riding you're going to do, not what kind of drivetrain you have. If you're going to do long road rides, you want the same things whether you have gears or not. Same goes for urban commuting, or offroad, or whatever. The only way the drivetrain matters is that it's maybe a little more important to have toe clearance on a fixed bike than with a freewheel (but it may not matter) and it's a little more important to have cornering clearance (but again, if you're cornering fast a lot you ideally still want that clearance even if you have a freewheel anyway).