I decided to start with component blueprints, because they're quick to research -- 3-4 months instead of 15+ for ship blueprints.
So I had to decide what level to research the prints to. For this, I used spreadsheets.
Anyhow, we can see that actual savings from ME research fall off pretty quickly. The 2.5 (now 3.7) million per tier 2 hull you save between my current ME30 prints and and ME90 ones adds up, in my case, to about 50 million per month for my entire production line. Still, having decent prints is a matter of professionalism.
I decided to go for 100/20. These are nice round numbers, plus in terms of resale, if you check contracts, it puts you at a nice balance point between poorly researched prints (e.g. 50/10) and excessively researched ones (200/50).
'Keep' means I'll be keeping both blueprints in order to increase production, rather than selling the one currently in production once it has been switched with a researched copy, and then itself researched to 100/20. This is because in the medium term I'm looking at increasing production to maybe 5 characters, which means I need moar blueprints.
Also of note, I've decided to tear up freigher production permanently. Even when one of them (charon, of course) is pulling much larger profits than normal, the margins are still pathetic compared to jump capable ships. Plus, this is a good time to sell freighter prints -- my charon BPO went for 72% over NPC price.