I'm not sure what you mean by competitive--because it's a program where students work together, not against each other. I don't think the CSD curriculum at Northwestern is hard at all, and I've taken around 8 graduate-level courses. I actually think the program tends to "dumb-down" certain concepts for the graduate level students, especially for those who have no science background. If you work hard and put effort into each course, you will likely get a B+ or higher in all of your courses. The science classes (anatomy, voice, dysphagia) are known to be hard classes--but if you study, A's are possible.
As an undergraduate student, I was super involved in extra curricular activities and definitely put school on the back burner at times. Even then, I still averaged a 3.9 in my CSD coursework. I have no doubt that if I put 100% of my time into school I could've gotten a 4.0. I think that's possible for anyone if they put their mind to it.
I hope this helps!