It appears some bench tests have been done using Windows on the iMac and the results are FAST. http://news.com.com/2061-10794_3-6058301.html?part=rss&tag=6058301&subj=news
Also note the response called XP on MacBook runs Photoshop faster than Windows laptops
Also note the response called XP on MacBook runs Photoshop faster than Windows laptops