On one hand, it's important to try to get the right size tallit, so you don't have to struggle to keep the tzitzit off the floor and on the other hand you don't have a tallit that's too small on you. Some people like a tallit that's long and elegant, while others prefer small and easy to keep on your shoulders. Here was one inquiry from the latter type, who seems to me to be a bit extreme in his thinking. 

Shalom,
The Beit Yosef Tallit looks very good but I do have a couple of questions.
I am 5'9" but regardless of size charts am thinking about getting the size 45. Is that recommendable? I am looking for a "happy medium" that covers the back even if draped over the head, not a scarf type yet not the Chareidi style that typically gets very close to the floor. Thank you, Andrew

Going up a size or down a size is not a big deal. Some people think long is elegant; some people prefer it short and manageable. But the problem here is that Andrew is talking about going down at least three sizes. 

I told Andrew that someone his height would normally go with a size 60 or 70. A size 55 would be more manageable and a size 50 would be very easy to wear. But a size 45 would be rinky-dink, if you ask me. Usually a size 45 is for bar mitzvah boys hovering around the 5' mark.

If you want to be absolutely certain, I told Andrew, try to get a hold of a known size tallit and try it on. Every size down means four inches less in length. So if you try on a size 60 and see that it hangs down to mid-thigh on you, or maybe the top of your thighs, you'll be able to picture a size 50 hanging down eight inches less than that.

A size 50 is also going to be 10 inches less across, i.e. you have five inches less tallit on each side to bunch up on your shoulders. But for most people the height (i.e. how far it drapes down in back) is the critical factor in tallit sizing.