How "taxed" is the Zync 706 (7045) when running the AD-FMCOMMS5 board?

I see that the AD-FMCOMMS2 and 3 can be run by relatively small Xilinx FPGAs, like the 702 and others. But, the ZC706 board (with the 7045 900 pin chip) is needed for the AD-FMCOMMS5 board, which needs 2 FMC connectors and, apparently, at least the ZC706 development board from Xilinx. Is the need for the 706 because the power of the 7045 (and/or number of pins) is required for the COMMS5 board, or is it simply because 2 FMC connectors are needed for the COMMS5 as opposed to the COMMS2 or COMMS3 board? Given that 2 FMC connectors are needed for the COMMS5 board, how much extra capacity, in either computing power or available pins, is available when using the ZC706 (7045) Xilinx board (chip)?

Thanks,

Ed