I collected an X3 upgrade from Etcetera's shop in Stockport, Manchester yesterday, but because of the query raised in this thread about the Guitar Pro export to Sonar, I asked them to set up some X3 and Guitar Pro tests. (I had previously bought Guitar Pro 6 and the X2 upgrade from them, but had continued to use GP 5.2 because my old laptop could not run the latest version.)
 
I brought along GP 5.2 midi exports used to import some 60 songs into pre X series versions of Sonar. Virtually all these songs were developed completely in Guitar Pro and had been imported into a Sonar template to record audio. (The original procedure had not been straightforward and a standard Guitar Pro template had been created to mirror the Sonar template. Also the deletion of GP control code events from the midi data after Sonar import had proved to be necessary.)
 
The tests showed X3 imported all the GP 5.2 midi exports tested into the Sonar template, just as the earlier Sonar versions had done. However, X3 also opened the midi files, even those not created using the standard GP template, and it assigned the correct TTS patches by default. The projects sounded OK e.g. the drums were not being played by piano.
 
Tim Burwell of Etcetera demonstrated TTS patches were assigned by default  because there was no midi out on his demo system, so it may still be necessary to insert the soft synths and select appropriate patches before Sonar projects play on working systems. He showed the GP 5.2 midi exports could also be opened with Mixcraft and its own patches applied by default.
 
When GP 5.2 midi exports were transferred to Guitar Pro 6 and re-exported X3 was picking up the markers from the GP 5.2 files. We were unable to check what happens when Guitar Pro 6 sound banks are used and midi is exported, as banks were not installed on their demo system. 
 
Thanks to Peter Butler and Tim from Etcetera I'm confident I will be able to import my Guitar Pro 5.2 works in progress into X3, and begin to use Guitar Pro 6 as well.