I've only ever run with one pen-name, Brett O'Neill, for a magazine that wanted to run a separate stream of features from an apparently American correspondent. It was also a nod to my family, who started to adopt my mother's maiden name of O'Neill. Even my stepfather married into my mother's maiden name, though since his own given name was Pratt that was understandable. I once added a 'J' to my name, Martin J Goodman, to avoid confusion with other Martin Goodmans that stepped onto the scene. Another Martin J Goodman emerges, so I gave up that pretense.
For success, as Michael Allan suggests, brand yourself by sticking to one tight element of one genre. Like him, I enjoy writing across all categories - that's my schtick. The new novel I'm writing takes me into children's fiction (I believed Michael Allen was having success with one such book, The Tunnellers, though can find no listing for it on his site so maybe it's another alias, I'll check; and Phillip Pullman recommends children's fiction as an area where your readership does not worry at all about you crossing genres). Since this new novel the first of a possible sequence I may yet rebrand myself as M.J.Goodman. Is that daring, or what!