How Similar Can Brand Names Be?

I have started my own clothing company called Evil Genius. The problem is that there is another clothing company with the same name which they trademarked in 2006. Their website is not called Evil Genius though, they have another company name but, it says The Evil Genius Store on the web page. I have also bought the domain name www.evilgeniuswear.com. I realize that trademarked names cannot be confusingly similar but what are the guidelines for this rule? Could I call my company Evil Genius Wear? The Evil Genius? Evil Genius Limited Wear? etc? Thanks in advance.