good brushless setup advice

[secondwaiting]

well here's what im debating...either

- Feigao brushless motor 540 8xl w/ RC-Monster Brushless Heatsink/clamp
- Castle Creations Mamba Max ESC
- External BEC/UBEC
- (2) Lipo 5000HV 2S 7.4V Packs


- Neu 1515 2.5d/F Sensorless Brushless Motors w/ RC-Monster Brushless Heatsink/clamp
- Quark Monster Pro 125B Brushless Sensorless Speed Controller w/heatsink
- External BEC/UBEC
- (2) Lipo 5000HV 2S 7.4V Packs


i'd rather do the MM/8xL of course because it's cheaper but im worried that i'll overheat it in arizona and ruin it. if i did go with that would it need a fan?
and are those batteries okay with both set ups? would lipo 8000HV 2S2P 7.4v packs give me more power or speed? or just better run times? should i go with a higher voltage?