1 battery vs 2 batteries that equal the same mah?

I have a question about batteries, seeking real-world experiences rather than theoretical math.

I am considering using a single 10,000mAh 4S battery instead of two 5,000mAh 4S batteries to extend flight time for my 690mm photography rig. Both setups would have the same or similar C rating.

Here is the comparison:

  • Two 5,000mAh 4S (25C) batteries: 125 max amp draw, 10,000mAh, ~1300g
  • One 10,000mAh 4S (25C) battery: 250 max amp draw, 10,000mAh, ~800-850g

I need about 115 max amps, so both setups work in theory.

My main question is about flight time and voltage sag. Will the lighter, single 10,000mAh battery provide more flight time due to weight savings, or will it experience voltage drop-off sooner compared to two 5,000mAh batteries?

In other words, do two batteries maintain voltage better than one larger battery in the same flight conditions?

I am looking forward to hearing your experiences.