I could not for the life of me play this Bass line passage on my midi keyboard at the original tempo. I slowed the whole project down, checking the preserve original pitch menu item for all the audio that I had recorded. Then I thought will REAPER let me record midi at the slower tempo and then speed it up automatically when I go back to the original tempo? I recorded a midi take perfectly albeit at the slower tempo, double clicked the speed slider to return the song to the original tempo and that's when a tear rolled down my cheek. A tear of joy.