I gave stacking extenders a quick try today, it was very overcast so not the best light. The combo struggled with AF a bit but live view focus was very snappy. I did not try infinity focus as it started to rain. I will use this combo again in good light when I get the chance. I used the 1.4x and the 2x with the 12mm tube to connect them. This lens just keeps amazing me.
Here are a couple.
This was handheld (resting on my knee) @ 1/250th f8
