Danial,
QOS does not work like this unfortunately. Even though QP8 is a higher priority than QP1 the switch will not empty QP8 fully before it starts passing QP1 traffic. For example, the switch will send 8 packets from qp8 and then 1 from qp1. This example is not exactly how it works nor is it to scale. There is a much more complicated algorithm used to implement the prioritization. I wanted to give you an idea of how it works.
On an over utilized port it is unknown how bursty the traffic is at any given time.
