For those that want a big sensor look on m43, Metabones is arguably your best solution. This Speed Booster XL review does a good job of explaining the advantage of using a Metabones adapter over cheaper knock offs. Metabones adapters are generally very well regarded, but by all accounts the Speed Booster XL performs very well on the GH4 and I can’t wait to see how it performs on the next generation of m43 cameras.