Never had any performance issues with limesurvey or phpsurveyor. It is simply not an issue. What is much more difficult is to find people who like to take part in a survey.

The main requirement for a system running limesurvey is low energy consumption since it will probably be running 24/7. For this reason I've been running phpsurveyor during some years on a pentium 200 MHZ box. It consumed a decent 45 watts. Performance was great. A nice choice now is to use a mac mini, eventually running linux if you like, since these machines are very energy efficient.

If you are running Windows you might see a less good performance due to the activity of the virus scanner.

Thanks for sharing your experience with us!