I Have similar problem, GTX 1080 MSI Gaming X but a I5 4690 CPU, get a lot of performance inconsistencies in some servers, like the fps drops from 120 to 70 and even 56 sometimes, have no idea what's going on, some will say it's bottleneck but I can run other games on maxed out settings but BF1 seems to have problems like these, also my CPU is always at 100% use only in BF1, the weird thing is it only happens on some servers or if i have Discord running while playing the game, wish someone could help us with that as well.. Although in your case does the fps only stays at 90? or it drops bellow that... cause I wouldn't really mind that much if it's always at 90 since you can't notice that much.... but bellow that it really hurts the performance.. even on low settings that happens to me a lot.. in the end you should be just fine with that rig..