People who try to equate there RX pack to the TX pack will say this.
The TX pack's load stays pretty constant so this can be better understood.
The RX pack voltage will go from a relatively light load 100ma to a heavy load 10,000+ ma peak.
At the load of C/2 for a 600maH pack you can go down to 1.1 volt per cell with NO problems or fears.
Lets not believe me, lets believe SANYO.
http://sanyo.wslogic.com/pdf/pdfs/KR-600AAL.pdf
Look at the C discharge rate. TO drop from 1.2 volt per cell to 1.1 volt per cell. 20 minutes.
This is at twice the discharge rate of the 9C the pack will take 20 minutes to go from 9.6 volts to 8.8 volts
So do you believe the MFG or your flying buddies!
Choice is yours.