Li-Ion cell selection for Malkoff M60?

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I am going to do this "mod" but cannot decide on the cell to use:

SureFire 9P with M60 and 2x18650 Leef body

Although tempting to use 2x18500 and also considering 2x17500

What are the pros/cons of 18650 vs. 18500 vs. 17670 vs. 17500?
I've read the mAh capacities and I think I understand the size difference, but anything I am missing? I realize that Surefire 9P with 2x18650 Leef body is almost as long as the 2D M*g.

Second question, how many times can I recharge these Li-Ion cells? As many times as NiMh cells?

 

[MSI]

The advantage with 18500 and 17500 is that you can use 3 x CR123 batteries as backup. It is better to have primary batteries as backup since the backup batteries will seldom be used, and having rechargables as backup is therefore a waste of money.
With the 18650 and 17670 setups you cannot have primary batteries as backup unless you use a dummy cell, this is because the Malkoff's max input voltage is 9v.
Going for 17500 you will not need to buy the Leef body since they go fine in the 9P body. This will save you quite a few bucks, so you will have to ask yourself if the small gain in runtime is worth the extra price.

 

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Thanks for clarifying this.