Not sure about magnification ratios but my Pentacon has a 0.33 min focus distance.
Here are some good macro lenses in the M42 mounts:
- Super takumar 135mm
- MC Volna-9 2.8/50 Macro
- Takumar 50/4 (1:1 native macro)
- Industar 61 L/Z
- Takumar 100mm f4 macro
- Vivitar Series 1 90mm/f2.8 macro
- Industar 50mm f2.8
Hope that helps