Higher Voltage or Higher Kv

[LiqrSicc]

Ok guys I need somebody to school me on this. Let's say the motors I'm looking at have are capable of 60k RPM. I'm looking at 2 of them. One that has is 5000kv and one that is 2500kv. With the 5000kv I can run 3s (only capable of 12v max) to get about 55k RPM. With the 2500kv motor I can run 3s in series for 6s. At 6s it will reach the same RPM as the 5000kv motor. The dilemma is with the battery packs. I can run 2 3s 2000mah packs in parallel for a total of 4000mah. If I go the 6s route I'd have the same packs and run them series so I'd just have 2000mah. My question is since the 6s route will require less amps to achieve the 55k RPM does that also mean my 2000mah 6s setup will have close to the same runtime as the 3s 4000mah? Some somebody explain what advantages/disadvantages I'd have running the 6s setup over the 3s setup?