I find early age 1:1:1 between Income:BE:Pop is good. For mid age, I find 1:1:2 better. For late age (high sci totals, 1500 bpa or so) I find 1:1:3 to be a good guideline. If you also want distro on the lesser sciences... search for the thread, I had a breakdown out of 40 out there somewhere.
These values *are* backed by a simple simulation, as well as my experience. Said simulation *did* account for NW. (In fact it "over" accounted for it, since it only looked at OPNW and not OPA.) It was a number of ages ago now, it was human specific, and it of course was approximate only - but as a general "rule of thumb" it tends to serve well.
The main problem with high BE sci and drafting higher is that income gets borked, and now you are open to either a deep chain or a PK. If you really draft to high DR, a good kingdom will actually pull off a real PK, as to just the "econ kill pk" using FB. Having so few pes makes you really easy to put into super-overpop.
Pop sci, however, does just the reverse. As well as upping military, it increases the pes/acre a little, so your BE goes up, your income goes up, and you get *harder* to deep chain because a lot of pes will leave, leaving room for offense. The chain just makes the pop sci bigger... so even when smacked down to a really small size you can still hold a lot of military.
Of course... due to the diminishing gains in sci, there is a balance point. And there is a fairly large area around the balance point where it matters very little. I think more BE than pop is outside that "good enough" range... but it is still much better than not having the sci at all!