Generally, you should notice less diffraction in the DSLRs because they had smaller number of megapixels (5 for the E-1 through 12 for the E-5) than today's Olympus/OM micro 4/3rds cameras (either 16 or 20 megapixels). Using the calculator at
https://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.htm the diffraction for 4/3rds and micro 4/3rds sensors is:
5 megapixels (i.e. E-1) | f/13.1 |
10 megapixels (i.e. E-3) | f/9.3 |
12 megapixels (i.e. E-5, E-P1/E-P2) | f/8.4 |
16 megapixels (i.e. E-5 mark II, E-m10 mark III) | f/7.3 |
20 megapixels (i.e. OM-1. OM-5, E-m5 mark III, E-m1 mark III, E-m1x. E-m10 mark IV) | f/6.5 |
Now, this is only the theoretical estimate for when diffraction starts being visible. In practice, you can typically go 1-2 stops beyond that.