Steve and Ray, thank you for your wise words. Very much appreciated and very helpful.
I should add that the main reason I use Barlows is to make the planetary images bigger. They may be blurrier but they are still bigger. A 5-6 pixel disc is just not much to look at, in my opinion. See for example my images of
Mars with 2x Barlow and 2x + 3x stacked Barlows. I like the last one much more.