Be careful, the "Click to Run" version does not support much ActiveX. See http://office.microsoft.com/en-us/excel-help/click-to-run-known-issues-HA101850565.aspx
There is no OCW12 or later; 2007 was the last supported version. A new architecture was used after that; see http://msdn.microsoft.com/en-us/library/ms582023.aspx. I am not familiar with the differences between the various choices.
