Is this the R5 with the 1080 or 1080ti?
Both are comparable cards, and I am basically running the same system as you (Alienware as well), but I do NOT have any significant FPS impacts.
In fact, I just had the following review come in from someone with a MUCH lesser system than you or I have: "First impressions is that there IS an insane amount of detail with no noticeable hit on my laptop (MacBook Pro, Mid 2015). I thoroughly enjoyed doing a memory lane lap around the old patch."
I suppose it would be difficult to apply everyone's scenario to one another though. Some people love to try and slam the sliders full right, and that's unrealistic expectations (nor is the trade-off usually worth it when it comes to gain in visuals vs performance impact)!