It depends on the speedbooster you have. Metabones has a line of speedboosters specifically for the Blackmagic Super-16 cameras (original Pocket and Micro Cinema), which won't cover the whole sensor in the BMPCC 4K. Check the Metabones site and you'll see the models they provide for the 4K. https://www.metabones.com/products/?c=blackmagic-MFT
You can of course use that same lens.