a nikon-m43 speedbooster and an 11-16 is roughly the same cost as a panny 7-14.
Panasonic 7-14's only advantages are width(14-28mm) and weight(think it's like 10 ounces)
but the 11-16 is a (15.62-22.72mm) weighing in at near 30 ounces IIRC(inc speedbooster)
there's of course the huge advantage of it being f2(with booster) vs the f4 of the panasonic, so it really comes down to weight, speed and image quality(haven't seen comparisons but I hear the 7-14 is an amazing lens, and I know the 11-16 is, I'm just not sure what effect the speedbooster has on it.
Of course there's the other advantage of having a speedbooster, so you could adapt a 35mm f/1.4 to get a 49.7mm f/1.0
I was actually thinkin about it yesterday(not thinking about buynig one) and I thought to myself, do I really need lenses that fast often? and for me the answers of course no. I can get by with f/1.7.