How would you test which mobile menu pattern works better?

I have three mobile menu patterns I want to find out which one is easier/faster to use, ie, 1) top nav that pushes main content down, 2) top nav that takes over the whole screen, 3) side menu drawer. For both of the top nav patterns, they work as accordions to show the sub nav; For the side menu drawer, there is a second sub nav page in the menu, users can hit "back" to go back to the top nav list.

My test method is a between group test, each group of users(5) will use one type of top menu pattern (prototypes with the same content) to finish a few tasks that involves using the menu.For instance, find FAQ page(the FAQ lives in the top nav), find contact page (lives in sub nav). The data I want to collect is time on task and user satisfaction.

I have two questions, 1) How would you improve the test or would you approach it totally different? 2) This test doesn't reflect the amount of nav items may also influence user performance, eg, maybe nav with a lot of items is better for the top nav pattern that takes over the page. How can this be incorporated in the test or should it be another test?

Thanks!