I use the 4 or 5x loupe to judge the overall composition of the slide. For enlargement, my experience is that the slightest blurring, handshake or out of focus shows up. The rule I use is that if the final print is x times the film image size, the loupe should also be around x times. For 35mm full frame printing to 20 in by 30 in, one would need 15x to 20x loupe. For medium format, the same rule applies. They are useful only for viewing sharpness because the extent of vision is limited. But even a cheap 15 x loupe saves a lot of money lost on unsharp enlargements. I use a very cheap Peak (Japanese) 15x loupe. The 22x is very limited in field of view. For 8x, I use the Rodenstock. Good luck for your enlargements.