They're basically the same heat range. The 'R' just means it's a resistor style plug. You should probably be using a resistor type of plug unless you happen to have resistor ignition wires to reduce RF interference. On your vehicle there probably aren't any electronics to interfere with other than accessories like stereos and cell phones, so it probably doesn't matter. Of course if your tach has failed and you need to listen to the radio static to know when to shift then that's another matter.

As George pointed out, BP5HS is a hotter plug than a BP6HS. For NGK plugs, the heat range numbering scheme is opposite to most other plug manufacturers where a higher number is a hotter plug. For more info on heat ranges you might be interest in this NGK article.