QSFP versus SFP+ options - 3850s

[gp1200x]

Looking over the options for 40G connections I saw one option was a QSFP to 4 SFP+ connectors. What exactly is the logical advantage of a QSFP versus a port-channel in a 3850 using 4 10G connections. It seems that most of the QSFP options utilize 4 paths between the transceivers. Does this mean that it would be the same type of connection logic that a 4 port etherchannel might use - where individual end to end communications actually flow over a single path and new connections round robin over the four paths. Due to the price of 2 40G transceivers and the 40 modules for a 3850, I am wondering why I just don't utilize 8 10G connections between the stacks and save a lot on the modules and transceivers.

[fiberstorejames]

I really don't understand how you can use 8 10G connections between the stacks for 40G network.

QSFP+ to 4 SFP+ connection is mainly layout between 40G and 10G migration. You can use QSFP+ to SFP+ DAC cables or MTP to LC breakout cables to realize the connection between 40G and 10G switches. 

As for the high price of the 40G transceivers, maybe you should avoid the original brand and go for the third party optical modules. Cisco QSFP-40G-SR4 from fs.com is $55 

[gp1200x]

My point was this.   I need two 40G connections in an etherchannel for each stack just in case to provide redundancy in the event of a switch failure so that gives me an 80Gb etherchannel. The network modules are $5K each and I need two per stack...plus the transceivers so that is already $10,600 per stack (and I usually do use FS.com). Or I could buy two 4x10 network modules  and 8 AOC cables for about $4700 total per stack and that would also give me 80Gb if I etherchannel all 8 paths together. At the main stack I would use XS switches so I have plenty of 10Gb transceiver ports available and don't need as main 2x40G network modules there either.

Price wise the 8x10Gb etherchannel (80Gb total) is a lot cheaper.... versus the 4x40Gb etherchannel for each stack. So my question is what real advantage would I get having 2 40Gb uplinked paths versus 8 10Gb uplink paths as far as performance for the stacks?