I have found some updated info. On Anandtech, I spied an article about Nvidia's chipset for M/B's which will support dual PCIe x16 slots. It will also share one x16 channel between two x16 slots, as with the VIA solution. But they explain that current generation cards do not require the full x16 channels. AGP8 has a theoretical throughput of 2.1GBps half Duplex. But a PCIe x16 slot with only x8 channels has a maximum theoretical throughput of 2GBps Full duplex. So my original concerns seem unnecessary.
So roll on guys and finish your boards. I have found my new system.
Geoff.