This is the test mesh I used, 25K verts, non-nanite - it seems to be a good all-round test mesh for things like this:
I’ll try something with a larger tri count.
Edit: I was able to get one scenario where SMs outperformed ISMs - non-nanite - mesh with 150K verts - 3200 meshes on screen - zoomed out - lumen turned on - changing any of those flips it to ISMs being quite a bit faster.