Well, I guess I have to keep pondering then. Thank you all again!
A converter sure saves a lot of weight but those are expensive grams. Fortunately, I'm in no rush as the rain will be pouring down the next 4-5 months and I'll be working way too much. My next big goal is to shoot puffins up north in May and I'd like to be able to frame a little tighter than I can today.
Something struck me today when I was reading comments on these lenses. The makro-planar is optimised for short distances, I can understand that, as well as a 100mm being optimized for longer. The question is how big the difference would be between a close-focused makro-planar and a 100mm focused on infinity with an appropriate extension tube to cover the same area? What are the advantages of the makro-planar (if there are any)? Contrast, resolution, sharpness?