Please follow this link to download section where by you will see the list of issues resolved in Aspose.Slides for .NET 5.8.0. There is induction of no new features and only bugs are fixed in the new version. However, these bugs persist in Aspose.Slides for .NET 5.7.0. You may decide on the basis of fixed issues that which version suits you. But, I also like to comment that the customer support is always processed on the basis of latest available version.
Please visit this link to see the list of issues resolved in Aspose.Slides for .NET 5.8.0. The next release of Aspose.Slides for .NET is expected for release by end of January 2012.