From Engadget
At what length do DisplayPort cables start giving you trouble?

If you're on the market for a new DisplayPort cable, it's worth keeping in mind that longer doesn't always mean better. This length is when trouble begins.
TechBlastTechnology. Unpacked.UK & world technologyFrom Engadget

If you're on the market for a new DisplayPort cable, it's worth keeping in mind that longer doesn't always mean better. This length is when trouble begins.