I do my MPT2 coil heads with 30ga Kanthal. If annealed first, I get a nice tight coil no problem. The 28ga Kanthal takes 12 wraps and just won't fit well in the cup. With the 30 ga I only use 8 wraps and it fits great.
34g Kanthal? Man thats def not an enjoyable build to do. Anything 32 and over really doesn't hold its form good enough for me to bother with. If you try to make a tight micro coil it springs, and unravels and just isnt fun to use. 28 and 26 guages are awesome though. I'm sure it wouldnt work on rebuilding stock coils with wire that big, but when you get into pure rebuildables, def go that route. Much more of a pleasure to work with.