A little bonus value for this post... the perfect ratio for your picture to fit into the Steemit thumbnail is 3375 (width) by 2000 (height). It can be as big or small as you want, the site automatically will shrink it to fit.
I used to get so frustrated when my image wouldn't "fit" the picture frame right... now it's no problem.
I still get frustrated @heymattsokol lol ... I been messing with 800x460! Those are good tips, I might have to try out that ratio! :)