Will let you know!I will be interested in what both of you think of the 2x as I am somewhat conflicted about it. I have zero issues using the 1.4x -- to my eyes it is as good as the lens by itself in all areas. However with the 2x, I first see a tiny bit of IQ loss, arguably not enough to really matter for most images, but notable nonetheless. My bigger issue with it is what I see it does to bokeh; to my eyes it seems to clump it up --and rather significantly-- for lack of a better explanation.
Haven't had a chance to play around with it much but so far it seems to do what I need it to. The 1.4x doesn't provide enough extra reach for me to justify (at least at the moment) so I just went with the 2x only. As we all know and as @ptomsu pointed out, it's the only option to get 400mm with native glass right now, so I'm happy enough to have the extra reach without having to plop down $$ for another lens right now (or explain another lens purchase to my better half ). I should be able to play around with it more next month.