As I know, there is no special 3D benchmark for MorphOS.
Except the Cow3D, but it tests Warp3D, which useless and obsolete on MorphOS. (I also found, that on Efika + R2xx cards Wazp3D with HW rendering is significally faster than Warp3D)

The best way is to try 3D games for it.
I made some AmigaOS - MorphOS comparison
here. It is in Czech language, you can translate it with
gtranslator. And as I see, the translation is worse than my English.
[ Edited by sailor 17.03.2021 - 09:31 ]AmigaOS: Pegasos II, Sam440ep-flex, Micro A1-C, AmigaOneX1000
MorphOS: Pegasos II, Powerbook G4, iMac G5, Powermac G5 Quad