Performance settings?

So far I have not managed to render the full time line. At some (random) point Kdenlive bumps out with no error message. What would be nice (for debugging) was it did not take hours only to get up to that point of no result. What do you do to speed up the rendering process?

- Rendering threads = 8 but System Monitor shows CPUs oscillating around 50% load with only the occasional spark up ... I wouldn't mind if the CPU capacity was more solicited.

- RAM: out of the 4GB available it uses depending on rendering format MPED ~2GB, H264 ~3GB only. Especially for MPEG there's still some untapped capacity ...

So - what are you pro's doing to speed up rendering?

Intel® Core™ i7-2600K CPU @ 3.40GHz × 8
Embedded HD3000 GPU
4 GB RAM
Ubuntu 12.04 LTS
~10h rendering for ~1h worth of mkv remuxed mts clips

Thanks!