Both the PB1i's and the Fact 8's are superb speakers but have a quite different balance of strengths .
I have owned the original PB1i's for over two years and I am still constantly amazed by just how incredible they are .
They go very deep in the bass and I mean VERY deep , I fully believe the spec's when they say they go down to 24 Hz but It is not that one note thump that you get from most other speakers or subs but instead they give a slightly softer textured detailed natural bass that is so realistic .
Bass instruments are easy to separate and identify and each instrument has it's own identifying character , this acts as a platform for the mid range which is very strong and detailed and maybe a touch forward but never harsh .
The top end is detailed and equally balanced with the rest of the sound but beware of putting the speaker too close to any hard surfaces such as a side wall because the wide dispersion design of the tweeter can cause the wall to act as a reflector .
The dynamics the Pb1i can reproduce are nothing short of astonishing even at relatively low levels but when the wick is turned up it sound pretty close to live music with the right recording and source
I have heard the Fact 8's and their balance is quite different , they are much much lighter and a little tighter in the bass region but with the right recording the soundstage and detail is amazing , they can't deliver anywhere near the power and weight that the PB1i can but they make up for this with delicacy and ultra detail , I can see why so many people love them .
As always the only way to see which one suits you and you room is to try them at home but either way you can't go far wrong , I am surprised that you have not included the OB1i for audition . The OB1i would be ideal if the PB1i overpowers your room .