At Maccreate, there are 2 separate articles on comparing Aperture and Lightroom speed head to head.
The first article by Thomas Boyd titled ‘Aperture 3 Workflow Faster Than Adobe Lightroom 3’ with an update based on Adobe’s Tom Hogarty’s comments. There is also a video showing the entire process. Aperture managed to accomplish the import, evaluate, edit and export process of 600 Canon RAW files in 8 minutes. Lightroom on the other hand took 19 minutes for the entire process.
The second article by David Schloss ‘A Different Look at Aperture 3 vs Lightroom 3 Speed (Faster) But not 4x’ is about re-running a more controlled test like the first one with 121 Nikon RAW files. Aperture finished processing 121 RAWs in 5 minutes and 35 seconds while Lightroom took 8 minutes to do the same. A side-by-side video of the whole process with the two apps is also available.
Good news is both apps do work well under stressful environment.