Final Cut Pro (FCPX)- Scrolling credits speed How can I set the speed of scrolling credits? For example, I want to set a consistent duration of time that it takes from the time a name appears at the bottom of the screen to the time it takes for it to disappear of the top. 

I don't want to just estimate it and drag the duration randomly until it LOOKS about right. I want to set a consistent scrolling speed regardless of the number of names I may have to scroll through.
The built-in Credit Tile from FCPX does not work like that. As far as I know, the scrolling speed is determined by the duration and the amount of text. 
So if you have a long duration and few text the scrolling speed will be slow and vice versa short duration and lots of text fast scrolling. The Tile makes sure that all text is shown in the duration given. 
You might consider to try and make your own copy with Motion 5. Left Click on the Tile >> "Open a copy in Motion" or go for a 3rd party Title or Generator.