.... kinda. Not really. Sort of.

Yes, having PCIe gen5 lanes are good - if you have devices that can make use of that. Few devices can. Some new NVMe SSDs can; some extremely high end graphics cards support gen5 lanes but don't really use more bandwidth than gen4.

But there can be issues. For example, my AI lab is using an Asrock Taichi AMD motherboard which has two physical x16 slots. The CPU I have - a Ryzen 7 9700x - gives it the most PCI-e lanes it can handle, but even so, I still have to bifurcate the x16 physical slots into an x8/x8 config in order to use both GPUs:

root@lab:~# nvidia-smi -q | grep -A9 "GPU Link Info"
        GPU Link Info
            PCIe Generation
                Max                                    : 4
                Current                                : 1
                Device Current                         : 1
                Device Max                             : 4
                Host Max                               : 5
            Link Width
                Max                                    : 16x
                Current                                : 8x
--
        GPU Link Info
            PCIe Generation
                Max                                    : 4
                Current                                : 1
                Device Current                         : 1
                Device Max                             : 4
                Host Max                               : 5
            Link Width
                Max                                    : 16x
                Current                                : 8x

The cards are pci-e gen4, and they are capable of x16 @ gen4. But because the chip and motherboard can't do enough lanes, they're limited to x8 @ gen4.

So effectively, since I'm at x8 @ gen4, that's the same bandwidth available as x16 @ gen3.

This isn't a huge deal for gaming - the cards perform within a couple percent in gaming benchmarks when clocked down to pci-e gen3 vs. full speed at gen4. But for AI inference, it does mean I'm leaving performance on the table. I'd be able to get probably 10-15% more tokens/sec if I could run the cards at full speed. I just couldn't justify the cost of a full workstation motherboard and workstation or HEDT CPU to get two x16 @gen4 or gen5 lanes, plus still have lanes left over for the NVMe SSD.

And at this point, I'm using all of the PCI-e lanes that are available, except the ones for the "extras". My NVMe SSD is pci-e gen4 x4, and the two cards are running at x8 gen4. If I wanted to add another GPU, I would have to get an M.2 to x16 adapter (which exist; I have one), and move the SSD to an m.2 slot that's connected to the ... whatever it's called now, the "southbridge" or whatever, so that it wouldn't be connected to the CPU directly and would be competing with USB and SATA and the audio chipset and all that junk. Technically, that would mean I could use the SSD's current slot for the m.2 adapter - but even then, it would only be running at PCI-e gen4 x4. Plus, loading model files from the SSD into vram would be noticeably slower, so if I had to do any swapping of models in and out of vram, I'd be adding probably 500ms - 1s to my ttft, because of that southbridge bottleneck.

Anyway, tl;dr: faster PCI-e lanes is good but doesn't always solve the issues, and really only matters when you have hardware that can use the latest gen. Given all else equal, i'd rather have 2x the (current_gen - 1) lanes than 1x the (current_gen) lanes.