I hate noise from the PC, so I've sited my PC under the desk at the opposite end of the room to where I sit (so about 3.5m away). I have a pair of 5m DP cables running to my 2 ultrawide monitors without any problems at all, so it seems if you buy decent cables it just works with DP too.

The only potential issue is that they seem to be slow waking up from sleep. I've never been interested enough to investigate if moving the PC closer with shorter cables fixes that, or whether it's just an issue with having 2 monitors. I think the underlying cause is actually just because it's Windows and that one monitor (they're supposed to be identical) seems to wake up earlier than the other, so it briefly flashes on, then goes black while it reconfigures for 2 screens and then on again.

But anyway, my 5m cable runs seem fine. They weren't especially expensive nor especially cheap cables, IIRC around 10-15 GBP each.