the r710 has two pcie riser cards each with 2 slots. so there’s a total of 4 slots of available. unless..an optional pcie 16x riser card is installed (which only has one slot).

i imagine the typical setup is riser1 with 2 slots of pcie 4x. riser2 with 2 slots of pcie 8x. riser2 is closest to the power supplies and contains slots 3 and 4.

10Gbps NICs should go in slots 3 and 4 (max two 10Gbps NICs in one server).

pcie 4x full duplex bandwidth = 2GB/s
pcie 8x full duplex bandwidth = 4GB/s
10Gbps = 1.25GB/s or 2.5GB/s full duplex