Here is what your sound levels delivered to your ear with inputs of 50, 65, and 80 dB would be estimated at with three different formulas using an M receiver:
SmartFit - propitiatory Signia fitting formula
NAL-NL2 - Common standard formula across the industry
DSL v5 - Another less common standard formula
They all are probably going to sound quite different. The SmartFit would be the least aggressive, and the DSL v5 the most aggressive.
One possibility if you have a cooperative and experienced fitter would be to put one fitting in the standard Automatic program #1, then put the other two in copies of the Automatic program but with the different fitting formulas. That would allow you to easily switch between fitting formulas by just making a program change. Not 100% sure it can be done, but I think it can.