On average, I was reading around 20-25 articles per week just for coursework, and anywhere from 0-10 per week for my own research.
Of that, maybe 150-200 or so were relevant to my qualifying exam a couple months ago. I was lucky enough to have more senior students tell me to write quick summaries (half a page [at most] to summarize the takeaways of each article) while taking courses, so it made prep quite a bit easier. My Marketing Strategy class had us read 55 papers in 8 weeks, which definitely seemed like a wake-up call since it was our first quarter in the program. The time it takes me to read a paper with decent proficiency has gone down from 2 hours to about 45 minutes (longer, of course, when I go back to highlight/annotate).
For my first year research paper, I have maybe 200 citations in my Mendeley folder with a few dozen finding a spot in my text (I added citations into the folder based on title/abstract alone; many ended up not being too useful for my paper).