5s or 10s A123 setup for boat?

[gimpygolden]

I'm thinking of building another brushless boat and considering 2 different setups.
I have the A123's ,actually Linc is building me 4 5s packs right now

Should I run 5s2p(4600Mah) with a 1700kv motor or 10s1p(2300Mah) with a 850Kv motor.
Battery setups will weigh the same either way and take up the same space.

Equipment wise the cost is not much different if looking at comparable components for each setup. Motors are the same price either way looking at 70mm Medusa's, and as for the Ecs's
the Turnigy 80Amp Hv is $75 plus &25 for a ubec Vs. the $70 for a Turnigy 120A.
The 80HV is good for 12s Lipo /45v and my 10s A123's are only 33v so theres a bit of head room there.

Any input on which will be more efficient and yield the longest run times, All the guys over at Offshoreelectrics.com seem a little spooked at the idea of High Volt setups so I wanted the opinions of those more versed in big power setups.