Driving two Dell UP2715K monitors

I have been using a Dell UP2715K happily with a Nvidia NVS 510 card. It drives the screen at full res (5120x2880) and 60Hz refresh without problems, using a pair of DisplayPort cables. The card is also able to drive two other (single-cable) monitors at the same time .

However, I have not been able to set up two of the Dell UP2715K monitors - neither by plugging them both into the same NVS 510 card, nor by having one card for each. The second UP2715K will do 3840x2160 only, despite being connected with two DisplayPort cables. This is with Windows 7 x64 and the latest Nvidia Quadro/NVS drivers (350.12 released 2015-04-14).

Does anyone have a working setup with two 5k monitors?

OK, an embarassingly simple solution - only one of the two DisplayPort cables was connected, so only 4k resolution was available. The UP2715K on-screen display shows two DisplayPort icons side by side, but that doesn't necessarily mean that both ports are connected, only that it will try to use both if possible.

So you can successfully drive two UP2715Ks from a single NVS 510 card.

Since posting this question I have installed a second NVS 510 card in the same machine and am driving a third UP2715K from that second card. I expect that driving four of these monitors would be possible from the same two cards.