My statistical data:
Out of probably 6-7 cars that I converted to electronic ignition via the MP kit (and for street use only, if that matters), most of which had MSD ignition boxes (either the 5 or 6), and over a 15-year period...

Only 1 displayed any issues that were corrected via rotor phasing.

Would the others have run better if I experimented with phasing? I don't know...

I'd file this issue under the 'things to keep in mind' category.