I briefly ran a Dell ultrabook with a backup lynx camera, no Identilynx, just a B&W camera. There was significant lag with a USB-to-Ethernet adapter. Enough that I dropped it after one meet. I couldn't accept the risk.
Maybe I'm misunderstanding, but it seems like you've got one coming in through RJ45 on the computer and another through a USB-to-Ethernet adapter? Is the Lynx gear coming in through the dedicated port? If not, I'd suggest that is the problem. Lynx is going to carry a significantly heavier data load compared to IPICO.