They both will hit the ground at exactly the same time. oh,...yes they will (another interesting but worthless fact)
but the boat tail will travel a few yards further before hitting the ground
generally speaking, a flat-base bullet will have more bearing surface than a boat-tail of equal caliber and weight.
more bearing surface = more pressure
more pressure = more velocity
What that really means is that you need to back down on your powder and work up a new load.
A higher ballistic coeficient not only aids in retaining velocity/energy down range, it also aids in wind resistance. We can easily predict trajectories with a few simple tools/knowledge..... but it can be really tough to predict the wind drift down range.
Like longbow said, out to 300 or so yards-we really are splitting hairs.
As fair as killing "better"...... I don't see how there could be any difference.
the internal design of the bullet (partitioned/bonded/soft/hard/ect) has the real say in which bullet kills "better". And that also is dependant on impact velocity.
On a side note, I do generally find it easier to shoot tiny groups with flat-base bullets. But I do have some boat-tail loads that perform just as good.