Fast pass planning

[StirlingSilver83]

Hi everyone! I am starting to think about which fast passes I want to get for which days. I will be traveling with my hubby and my ds8 and ds 20 months. My ds8 loves rides. His fav ride is test track. Anyways my question is about magic kingdom. Now I am planning on getting fast passes for all the non thrill rides. But my question is this sometimes my son is feeling extra brave and wants to do the occasional roller coaster (thunder mountain) or also splash mountain (I know not a roller coaster but we did this last time and he was on the fence whether he liked it or not). Anyways I am just wondering what everyone's experience is in getting these 2 particular rides as the 4th or 5th fast pass after you have used your initial fast passes. TIA!