(2)2s or (1)4s

hey guys

its been a while, been out of the hoppy for about 5 years now but i want to get back into it...poor cars are in the basement itching to get driven

my last project before i stopped rc was an FLM tranny forward conversion for my x ss 4.6...which is the truck i want to get running again

going to put in:
MMM 2 man when i left we were all dying for castle to get the original mmm out and now heres v2 and its waterproof!
2200kv castle-neu (dont want hpi-neu because the fat fins will be a pain with the flm setup)

my question is this:
with the flm tvps the battery goes inside between the tvs, not in external boxes...so i have two options for a 4s setup

1. get (1) 4s 5000mah 35-70c pack
2. get (2) 2s 5000mah 35-70c packs and run them in series for 4s

what would you guys recommend? is there an advantage to running two packs vs one? price wise its basically the same, and running in series i wouldn't get the "2p" advantage, so really it just comes down to buying two small packs or one big one. looking at turnigy nano-tech