I tested just about every "flagship" program when I was looking for a new DAW. Vegas, Nuendo, ProTools, Sonar, blah, blah, blah.
I settled on Nuendo. It took a beating like nothing else and the summing (IMO) was right off the scale.
As I understand it, Cubase SX uses the same audio engine as Nuendo.
KEEP IN MIND - These were only quasi-scientific subjective tests. There are some who like PT, others who like Vegas, Sequoia, etc. SO, your mileage may vary.