Does disabling VT-x enhance stability/performance

Well done for doing your research. I regularly use all three options.

1. (Use the “Import/Export utility”). This is the easiest because it combines the whole VM into a single file and transfers it over without issue pretty much every time. However, in my experience when creating the OVA or OVF file for export it throws away all snapshots and if done incorrectly can result in a VMDK file. When you re-import the VM you should be able to select what type of HDD file you want created, VDI or VMDK.

2. (Copy the entire virtual machine folder, containing the .vdi and .vbox files). This is my preferred option and although I have had to edit the XML file a few times it's been my own fault for messing something up. Make sure that when you copy the VM, you get ALL the files associated with it. The issues I ran into were when certain snapshots and secondary VDI files were in the wrong directory and weren't copied properly. If you copy all the files (and permissions) you should not have any problems whatsoever.

3. (Clone the VDI using “Virtual Media Manager” and then recreate a VM on the target machine but using the cloned VDI as the hard disk). This is less desirable because then you have 2 copies of a VM, and it can cause licensing issues, network issues, etc, depending on how you clone the VDI file.

In summary, I would definitely recommend option 2, just make sure you get all the needed files when you move it over.