On my foot I feel both boots are pretty close in lenght and width but the Iron rangers have more volume.
Most running stores REI etc have all of the superfeet available to try on and wear around to test out.
For my 1KM and IR I sized the same 12. I measure 12.5 on the brannock they both fit great with a midweight smartwool hiking sock.
The IR for sure has more room in fact I could add a thin insole with the same sock weight. Both Great boots!