Pressure is determined by total area of nozzles and bypasses (or leaks) in the system and the specific gravity of the fuel.
16 nozzles of the same area as 8 would be identical pressure. Atomization would be better as the droplets/streams would be smaller. Might not be a noticeable gain in performance however. It usually isn't.
One thing that can get you is that different orifice types that are the same size don't flow the same. The lead-in on the hole, the length of the hole, the surface finish of the hole - all determine actual flow. So, you might have an Enderle .032, a Hilborn #16 and a Kinsler 620...all should be pretty much the same area calculation-wise, but they don't flow the same...close, but not the same. Flow testing them would be one way to get good numbers for them.
For example, some place (like FIE) could test your 8 @ 100 PSI/.792 SG and conclude that they flow 1.51 GPM.
The 16 you chose to replace them with might flow 1.63 GPM. Among other things, that would tell you that the main pill size for the new nozzles will need to be slightly larger to drop the system pressure a few pounds to make the GPM output equal to the original 8.
Spud