BF-609 H.264 encoder optimization and related questions.

Greetings,

Attached picture shows single BF-609 core encoding performance when recording slight motion.
I have been experiencing an issue where motion prolongs encoding above 40ms threshold, somtimes up to 50ms. 
This benchmarks are done at 640x480 resolution, black and white video whilst splitting frame encoding between core0 and core1 (50%/50%).
The question at hand is the way to prevent this? since during prolonged motion buffers back up and dropping frames is not really an option.

Second question - when splitting frame between two cores, we get this nasty horizontal line where frame is split. Is there a way to avoid this?
I assume it is to be expected since encoding is done by two separate encoders instances but not to this degree. 

I will also attach video sample and encoder settings that are being used: