I have a set of Shimano 540s and have been very happy with them, but you'll find many poor reviews, especially from the heavier riders (I'm only 70kg) who have trouble with broken spokes. I think people expected too much from these wheels - they are only 105 standard, but because they looked good, they were often used as part of an Ultegra package bike to bring the price down slightly.
They are old stock now, so you can pick them up cheaply - more cheaply than the Ksyrium Equippe I would have thought.
The Equippe has a slight weight advantage and stainlees steel spokes (The WH540 has a steel spoke that can rust). Although I'm happy with my 540s, their main attraction at the moment is their price in clearence sales. However as a day to day wheel for lighter riders I think they are fine.