You might be able to increase speed for long loops by calling XSteam using arrayfun (http://www.mathworks.com/help/matlab/ref/arrayfun.html) or use IAPWS_IF97 (http://www.mathworks.com/matlabcentral/fileexchange/35710-iapwsif97-functional-form-with-no-slip)
@Daniel Vecchio - you might try NIST Chem WebBook (http://webbook.nist.gov/chemistry/fluid/), EES from the University of Wisconsin (http://fchart.com/ees/), TRNSYS also from Wisconsin (http://sel.me.wisc.edu/trnsys/) or Aspen (http://www.aspentech.com/products/aspen-properties.aspx). Good luck and post your findings to help others.
To get the help for both XSteam and XSteamUS, you need to open the source and delete the first three lines, or at least the blank lines. MATLAB will only return help using the first connected block of comments, but both XSteam and XSteamUS have a blank line after `%h_prho behöver T_prho för samtliga regioner!!!!` hence that is the only line returned as "help".