Like you said, I think PRX are really good in B03s and I can see the first game going either way, but it'll surely be a 2-1. I am going the Optic way because I really want them to be in the final first.
FPX vs FNC atm depends on map picks. If FPX don't ban Icebox this time against FNC, then imagine a Fnatic 2-1 and if Icebox gets banned then FPX may 2-1. I am predicting FNC to win here.
If PRX drops into the lower bracket I think they may have a tough time because they will play in a Bo5. Their map pool outside Ascent, Fracture and Bind seems not that convincing. If Fnatic gets Icebox and Haven into the map pool then it'll be a 3-1 in favour of Fnatic.
A grand final between Optic and Fnatic is the most hyped final and the final that most people want here at the tournament. FNC ban Breeze and Optic ban Icebox. Fnatic wins Ascent and Fracture. Optic wins Haven, Bind and Split to take the series 3-2