Seems to me the question you should be asking management is "Why do you want to change from an OSS Environment to Windows" ? Since you're already in an OSS shop the current and past performance of said environment already speaks for itself, if management has particular issues with the current environment that they think will be addressed by going to a Microsoft based solution, let them verbalize those and be prepared to show them how those same issues can be addressed with OSS solutions. I'd also keep in mind that the decision may be driven entirely by Microsoft Marketing their wares directly to management and thus it's rather easy to refute the typical Microsoft "talking points" one by one (Microsoft tends to sell based on very general statements with respect to how their products are superior to OSS products).