I think you need to sacrifise one roll from each speed to experiments. Take same image with 25 to 1600 speed and see how Swema reacts to developer.
People here often advises to use most diluted developer and extra long times for unknown films , you can buy adonal or rodinal and make these solutions with water.
Only you have to have , a small bottle and some developer in it , carried from home to public lab , adonal is cheap and excellent , HC 110 from Kodak is EXCELLENT.
May be It could be possible to do the same with sprint , but I dont know
Good luck ,
Umut