PCIe x8 NIC in PCIe x16 slot

PCIe Motherboard 4x pcie slot I was assuming they could all reach the 1000mbs that the pcie slot could reach Does anyone know of a PCIE 4x card that can get 900- 4x4 slot PCIe x4 is mostly for server grade network cards

4x4 super slot 13, Intel X299, 8 x DDR4 DDR4 4200+, 4 x PCIe x16 1 x , AMD 3-Way CrossFireX NVIDIA 3-Way SLI, na, CH HD , GLAN + Wi-Fi, 0,