Ok after reading some posts :

About the contribution of stuff and food / pots : Don't get the wrong idea. 1 more ilvl (more main stat) is roughly 0.6 % more DPS, and food + pot alltogether is only 0.6% buff. (source : Mike Matrix tool).
Without any offense (I insist on that I'm just stating not calling out), food + pots won't grant 300 more DPS to someone doing 4300, those differences between runs are to be explained on better raid buff window synchronisation, along with crits/dhits landing on your spikes rather than your fillers.
TL;DR : If 350 RDM are at 5k DPS on O6S (a fight with really good uptime and relatively poor mechanics wise), a 343 RDM should be aiming for only 5% less, so 4700-4800.

O1S and O2S are as "easy" btw.

Second point : If you're not checking you e-penis or wanting to play for the records (best DPS? best kill time, etc...), and you feel bad not having a great DPS, just focus on "what DPS is needed", and not "what DPS is expected by fflogs"

O6S requirements are somewhere like what, 28k rDPS ?
Means if the 2 tanks are doing 7k together, and heals 3k together, it leaves 18k on DPS to be dealt with, 4.5K each. Someone not doing 4k5 at i345, doesn't mean he can't clear it, but it surely means he's being carried into the kill by his teammates compensating the lesser participation. But if you're above 4k5 ? You're helping the team. So aiming for those 4k5 would be fine (but of course aim for the highest possible, what I mean is ignore pesky people if you at least do your part of the job ; only listen to advice, not trashtalk).