Got it. For those that might be having the same problem. When you go to the open with click on the solidworks launcher instead of the EXE. Than it will ask you what version you want to use and allow you to set it as a default. Works great
See the Restore File Associations section at http://help.solidworks.com/2013/English/solidworks/sldworks/hidd_options_fileexplorer1.htm
See also the last two posts (#6 & 7) at https://forum.solidworks.com/message/371689#371689
The following post explains how SW changes the registry to determine which version will open swx files
Open say SW 2010 and copy the reg key to your desktop name it sw2010
Now open say SW 2013 and copy the reg key again call it sw2013
Now you can set the reg keys to what ever version you need to work with.
You will find detail info in german here: