It would take a lot of cuts, but a herringbone design would create interest:

Doug, that must be a typo on your part - that is a partial basketweave pattern, not a herringbone :-)

My program doesn't have a herringbone pattern for granite blocks. The graphic shown was as close as I could get. As for the 6" gap, I'm assuming you are referring to the divider spaces between fields. In the dividers you can do many things based on your preferences, ranging form pouring concrete to 6" pavers.

The blocks are for between the 5' pads, not in them. So the blocks themselves are for the dividers :-)

My choice would be for the rectangular blocks, unless that is cost prohibitive.

Mock up a sample of the rectangular blocks and SEE if it is a pattern that YOU can accept.

I think the rectangular could look great for the banding, but you'll want to plan out how the joints align (or don't) at the corners, so it looks intentional.

Here is an example of rectangular granite cobbles in a running bond pattern to help visualize the material... sorry I don't have an example in concrete like you are proposing.

I am partial to 4" squares for this application. Squares would allow you to set 1 stone at the center of each intersection, making the Belgian block insets non-directional. Much better look.

Picture of finished area please.