Hey, if you didn't already paint all your minis I found great video with examples how you can use both speedpaints and various types of primed bases with zenithal trick for fast gradients: https://www.youtube.com/watch?v=gT2JV3Ks41g
And here you have practical example how speedpaint works differently on different base colour: https://youtu.be/WjfHiwczl84?t=182
He is infinitely cute.