_long_ PCIe extension cables

I'm looking for info about long PCIe ribbon cables + riser cards. By "long," I mean on the order of 3 - 4 feet. I've never seen them this long, so it's a two-part question: do they exist? assuming they do, would there be performance downsides (and how significant)?

I've googled+read a lot, but most conversations focus on normal-length cables and conclusions don't seem very… reliable/well-founded.

For context, I am planning a nonstandard layout where the GPU+other pcie components will be positioned away from the motherboard. Not literally four feet away, but I am considering cable routing, ease of maintenance, and so forth.

thanks!

Do they exist

Probably not, at that length you would have major timing issues with the PCIE bus, not to mention tons of interference.

they do exist.

thanks to you both.

any good source on performance considerations?