I’m having a slightly different problem. MBL is very quick while editing, my problems start with encoding.
I have tried different settings with H.264 output and it seems like pot-luck as to whether it succeeds.
When encoding, it locks up 90% of the time, then I have to click cancel, close Premiere, and then kill the Premiere background process to enable re-loading before I try again.
Rendering Entire Work Area doesn’t help either.
I have Premiere Pro CC 7.2.2 (More reel), MBL 2.5 on Windows 8.1 64bit.