They will push Fusion 6 as being ready for Mavericks and Windows 8.1. Having used them in the past though they are usually pretty good about answering tech support questions. The easiest and fastest way to get going is to shoot them the question asking if 5 will run Mavericks. Sometimes they may have an updated version that will run it but is not supported so you use at your own risk.
Compare VMware Fusion to Parallels Desktop | VMware Canada Although the link says compare with Parallels it actually has a comparison between Fusion 5 and 6.