You can query the page size propeties via code and you don't have to parse the XML. See the following link which contains a VB.Net RS script:
http://www.developmentnow.com/g/115_2005_10_0_0_616192/Probs-running-script-to-fix-linked-report-page-settings.htm
Converted to C#
ReportService2005.Property[] pageProps = new ReportService2005.Property[6];
pageProps[0] = new ReportService2005.Property();
pageProps[0].Name = "PageHeight";
pageProps[1] = new ReportService2005.Property();
pageProps[1].Name = "PageWidth";
pageProps[2] = new ReportService2005.Property();
pageProps[2].Name = "TopMargin";
pageProps[3] = new ReportService2005.Property();
pageProps[3].Name = "BottomMargin";
pageProps[4] = new ReportService2005.Property();
pageProps[4].Name = "LeftMargin";
pageProps[5] = new ReportService2005.Property();
pageProps[5].Name = "RightMargin";
pageProps = _rs.GetProperties(string.Format("{0}{1}/{2}", _mainFolder, _masterFolder, MasterReport), pageProps);