Don't get the 3600mah cells either, their amp rating is lower iirc
Get the 3500mah cells... nothing more... nothing less
The max current rating is the same, but internal resistance is a bit higher on the 3600mAh cells. This only becomes a factor at currents higher than 3amps, so for most applications isn't really a factor at all. For instance, they both provide 5A just fine, but you might see about a ~5% lower capacity in the 3600mAh cell at that current due to the internal resistance.
EDIT: I just reviewed the latest tests (2019) of the Keeppower 3500mAh cell and 3600mAh cell, and I see no difference whatsoever in capacity or energy between the cells, regardless of current up to and including 5A.
One thing to note for differences.
When using 2 li-ion cells: protected cells usually run flat(near full output) then completely dies once one of the cells reaches it's cutoff pt.
Unprotected cells usually run for a bit then have a constant decline in output. Or start off with a steady decline (depends on module)
Given the same module and cells (x2), I've never seen a significant difference in the runtime slopes of protected vs. unprotected. Yes, the protected cells will leave you in the dark when the voltage protection kicks in, but at that point you shouldn't continue to run the cells anyway unless you want to incur damage. I'm hoping you have an example plot of protected vs. unprotected to show that I'm missing something.
IMO, the solution to the cutoff problem with 2xLi-ion in these cases is to have a backup light (or cells, or both), rather than continue to run unprotected cells past acceptable low voltage limits. Better yet, monitor your protected cells and don't hit the cutoff in the first place if that is an option.