Yea.... the "S" in the case of the Gt2860RS is in the model number itself and not the turbo part number, but as you said once the cartridge number is the same the wheel size,trim etc. will be exact.
But....the cartridge number in the case of the -5 (446179-51) is not on the id plates to confirm such....if it was, there would be no worries.
Are we to assume that once it has that 707160 - 5 on the id plate whether with or without the "S" the cartridge number will automatically be exactly the same???