Open GL vs. Direct X Mode

My understanding is that one relies more on the graphics card for processing and the other on the software/processor.  My suggestion, try both and see which you are most happy with using.  Once you select one, it will default to that in the future.

Google Earth Pro vs Google Earth (free)

Google Earth Pro includes all the features of Google Earth along with these extras:
1.   An area-measurement tool (that measures square feet, miles, acres, radii, etc.)
2.   Data importing, which allows you to ingest up to 2,500 locations by address or by latitude/longitudinal coordinates
3.   The highest resolution printing and saving capabilities, which enable larger, clearer printouts (up to 4,800 pixels)
4.   Movie maker, which allows you to export movies of zooms and tours
5.   GIS data import, which allows you to drag and drop SHP files, GeoTiffs, etc.
6.   Premium printing, which enables you to print high-resolution images up to 11" x 17" (4,800 pixels)