You can customize the size of the slide which will change the size of the playback.

Start a new course and select a template. Click Module>Design Settings>Slide and type in the size of the slide you want to use. Remember to take into account what the playback environment will look like. I just resized a slide to 795x505 for a 1024x768 IE browser window because of the typical browser "chrome", start menu and LMS assets that take up space when the course is launched.

I suggest creating a small sample at the size you think you'll need and then run lots of test in the environment the course will be delivered in (this will get tricky if you will have little control over the environment - users may have diff. browsers, different screen resolutions, etc...)

I liked some of the elements in one of the templates, so I started with the specific CourseLab template, then resized the slide, then moved the elements around to fit on the screen and removed the unwanted elements.