Simplify3D has a great feature that overrides the print speed for layers that are below a specified duration. You can also adjust the percentage the speed can reduce down to. I use this feature all the time!
Temperature, however, also needs to be adjusted in step with print speed. You can currently do this manually by adding temperature setpoints based on visually ascertaining speeds from the print preview but this is cumbersome and unintuitive. Marlin has an Auto-Temp feature but it can only work with buffered Gcode so this feature is best implemented by the slicer.
My feature request would be to add a Temperature Override to the Speed Overrides settings. It would take the guesswork out of getting the temperature not too hot and not too cold for a perfect printing experience.