Performance for the new Intel powered Apple Mac computers is far less than the company promised during last week's unveiling.

The Macworld trade publication pitted the new Intel-based iMac against an old G5 model and found that the speed gains fell short of the promised results by a significant margin. 

Apple chief executive Steve Jobs boasted at the Macworld tradeshow last week that the new iMac would offer at least a 200 per cent performance boost over previous generation G5 systems.

"What is different is that the new iMac [with the] Intel processor is two to three times faster than the iMac G5," Jobs promised delegates.

Apple based its findings on two benchmark studies in which systems were tested in a controlled environment. But Macworld pointed out that such tests fail to reflect performance in real-world applications. 

The new Mac machines actually showed an average performance increase of 10 to 25 per cent while performing a series of everyday tasks with software especially designed for the new systems.

In a few cases the new systems showed an improvement of roughly 80 per cent, but this could not be attributed solely to the new processor.