I had the opportunity to drive both in February. The 2014 QP is amazing, the interior is more like an Italian version of a Rolls. The v8 is very powerful and effortless, instant power, locomotive torque. Fit and finish was flawless. I felt however, the Ghibli was more sporty and lighter on its feet, that, and the $45k difference is what directed me to the Ghibli. The QP is near S class huge and very luxurious, if that is what you want, and the price does not deter you, go QP. If you want a lighter, and a little more youthful look, go Ghibli.
No bad choice here, just personal preference, money, and world class driving. Drive safe.