x299 gives you 7x PCIe 3 x4 slots. That might be surprisingly good enough even for GPUs. And most motherboards can reconfigure number of lanes per slot. Now im

x299 gives you 7x PCIe 3 x4 slots. That might be surprisingly good enough even for GPUs. And most motherboards can reconfigure number of lanes per slot. Now imagine having an 8-slot motherboard for 3990X that could be configured to e.g. 4x PCIe 4 x16 or 8x PCIe 3 x16. Wouldn't you like such motherboard? For Deep Learning I don't really care about PCIe 4.0, but I do care about being able to fit as many GPUs in as I can (they talk to each other outside PCIe anyway). With TRX40 I am limited to 4 GPUs. Even PCIe 3 x8 is good enough for DL.