It depends on where you're shooting...If you wanted to double expose in full daylight outdoors, you would definitely need low speed film, and probably a pretty high f-stop and shutter speed to compensate. I was shooting indoors with ambient light, and in that case the 100 film was fine. I don't think an instant film under 100 was even available on the market at the time.

shortwave radio, that's a super interesting hobby! maybe as the digital technology becomes more popular the old sony radios will go down in price? As digital took over I ended up getting some really great film cameras for really cheap. unfortunately I cant find anywhere local to get film processed anymore...and my house is too small for a darkroom. One day perhaps!