500 watts should be plenty of power for general mixing as long as the motor has overload protection to prevent overheating during heavy mixing. If you intend to be using it for heavy cookie doughs or breadmaking I would go with no less than 550 and preferably 575. You do want to make sure it has overload protection in any case especially since it is an expensive mixer. I am not familiar with the Kmix but for the serious baker I would recommend you research Kitchenaid brand mixers in the US. I would buy a Kenwood sound system based on reputation over the years but kitchen appliances???? Not so much! If you are in the UK however you likely don't have that option. They seem comparably priced so one would likely conclude they are of similar quality construction. Hope this helps