Ok, now I understand.
Both the QS & The MDD can get the top Dual 7447 (1.8GHz), albeit from different companies. At that point, the MDD simply wins due to faster bus speed.
The QS seems to have it in the bag for ultimate clock rate / fastest 7448 with its 2.0GHz SP, which I'm guessing between the bigger cache and extra 200Mhz easily makes up for the slower bus. (especially since the only MDD comparison drops to a 7447 @1.8 on a slightly faster bus.)
Here's an interesting one though:
1.8GHz Dual 7447A in 167 MDD vs 1.7GHz Dual 7448 in 133 QS? Faster Hz, Smaller cache, Faster bus vs. Slower Hz, Larger cache, Slower Bus, More efficent Core