You answered your own question, Pavlov. Also the 2.5K can not do a crop window.
If you want fast frame rates you need to move to the Micro Cinema camera, for a look close to the BMCC, or upgrade to the Ursa Mini. Also, this is a "User" forum, if you want an official response from BM, you need to contact your regional BM Support office directly for a quicker response.
Cheers