Even at 3x Rads, 2 MB blocks, 1 CPU block, 2 GPU blocks and all that tubing to cover a massive case I am on the verge of needing a second DDC+ pump.
You will not benefit from a second pump, its quite likely to have a detriment due to the heat dump into the loop of the additional pump. If its for redundancy then I guess there is value but you do need to mitigate the heat.
i7 3930k @4.4, 2xMSI GTX 680, 16 4x4 GB Corsair 2133 RAM, Crucial m4 500GB, Benq XL2411T, Xonar D2X. All custom watercooled by 2x MCR 320 and 1 MCR 480