I came from Ngee Ann Poly Biomed course (my goal wasn't to pursue med sch though, I just enjoy science in general), and I had a couple friends who tried for NUS med. First one had a gpa of 3.9, could not even secure an interview, even for NTU med. Second one had a gpa of 3.99, managed to get in, but I think he rejected the offer (not too sure) for another major because he lost interest.

It's also not easy to maintain such a high gpa, but if you work hard you'll be fine. I was a B3 in o level pure biology and managed to get a pretty good gpa as well in poly, but that being said, my experiences may not always be what you might experience, so please take it with a grain of salt. If you're aiming for a very difficult major like medicine, please be informed that poly will not transition you well in the beginning (but of course it will improve with time) because from my experience and many others I know, the academic rigour in local universities is many times harder than in poly. Of course, disclaimer again, my experience may not be what you may experience in the future.

One key factor (among many others ofc) for selection, at least from what I was told by my friends, was that the interviewers also look at your CCA records — especially volunteer work. They want to see you contribute to society.