We have very similar dimensions for our vanity in our main bath. I think I am going to go with an 18" wide tower, which should leave room for at least a 54" long vanity, which is a good size with a single sink. I would determine what you plan to store in the tower and mock up and measure if they will fit. Are you planning to have drawers or roll-outs? That will take up more space too. I have an 18" pantry in my kitchen next to a 44" beverage counter, it doesn't look too large. I think you will be much happier with the extra 3" in your tower than on the counter.

I would do the tall 18" linen cabinet. I don't think it will look too big or out of proportion.

Thanks for the replies. I think I am going to go with the 18", especially when I think about having 3 extra inches of tower storage vs 3 inch of counter top!

Can you make your linen closet less deep than your vanity? Then the linen closet will set back a little and not look so bulky. You can find photos on Houzz.com.

Thanks, I'll take a look at houz. I didn't think about making it a little less deep.

My linen cabinet now is full vanity depth and frankly, it is a pain. Towels and sheets almost fit two deep, but you have to smoosh them in to make it fit -- then the ones in the back get lost. It would be even worse for bottles and such. You could put those things in rollouts, but only to a certain height, so I'd probably make the top less deep. I tested our 15x15 uppers in our breakfast room hutch and they were large enough for towels and sheets. I haven't don it yet, but am thinking we will do that in our master bath.

we had a large linen cabinet installed into our master br and i love it!! it is ~ 21" deep including the doors and i love the depth. it is deep enough to hold folded blankets completely and in one of the lower 'doored' cabinets, i removed the shelf and use it to hold a hamper.