DKT1001

I have 3 "Klipsch R-5502-W II in-Wall" speakers LCR (Left, Right front and Center Channel) and two "Klipsch R-5800-W II in-Wall " speakers for Back. Have Couple of questions:- Q1. Should I install Center Speaker Horizontal (Left and Right are installed Vertical) OR all three should be Vertical? Q2. R-5502 is little expensive than R-5800. If money is not constraint, If I replace 5800 with 5502 for back side also (that way I will have all 5 speakers same), will that give better sound quality OR it wont make any/much difference? Q3. My HT Area is kind of open from two sides. R-5502 is good enough? Q4. I got recommendation to replace R-5502, with THX series (like Klipsch KL-6502-THX) which is almost 3 times R-5502. Can I replace only center channel with THX while keeping L and R R-5502 (Will it timber match), or I have to replace all three? If all three replaced, should I mount all vertical or keep center channel horizontal? TIA