Recent performance tests conducted by Devil Mountain software show that Windows XP outpaces Vista by a two-to-one margin. Microsoft fired back at the report saying that Devil Mountain's OfficeBench software creates an "unrealistic" test environment by measuring tasks performed at "superhuman" speed. According to Microsoft, this type of measurement exaggerates small delays that would be unnoticeable by users under ordinary circumstances.

Not to be outdone, Devil Mountain has issued its response, stating that Microsoft's video demonstration of the Devil Mountain test was exaggerated for the purpose of discrediting Devil Mountain's test. Microsoft had asserted that the Devil Mountain tests merely opened and closed windows to measure performance. According to Devil Mountain, their performance tests included the generation of PowerPoint presentations, Excel charts, and a number of other tasks.

Microsoft's just-released service pack 1 for Vista may address some of the performance issues noted by Devil Mountain in its initial tests.