After running a bit longer than my initial testing, I did see improvements on my VII running 3x, but for everything else, I've always ran 2x tasks.
If you don't want to use an app_config, you could also use different preference sets for each machine. Default could be set at .5, and then you could set Home, Work, or School to .33. Just be sure and change the computer "location" to whichever set of preferences you want too use.
The down side to the above, as mentioned by mmonnin, is that the change does not take effect immediately. All of the tasks that have already been downloaded, will have to be completed before you'll start to see the machine running at the new setting.