It is a simple reality that more complex and capable renderers have more uneven performance that varies widely based on scene and lighting. While Firefly is far from a high end render engine, it is grown up enough for this to be true for it as well. The simple reality is that you are NEVER going to be able to ray trace very fast. You are ALWAYS going to have to make compromises in your scene if youw ant to animate it and keep render times low. That is a simple reality of the math. This is not limited to Firefly. Small adjustments ins cene and ligting can make a factor of 50 difference in render times for higher end renderers - and if you add radiosity and GI into the mix it gets more complex. FF is a different beast than the P4 engine. If you want the extra features you will have to work with it, like all the bigger engines - shader adjustments, light placement, bucket size, bounces and all the rest of it. If you DON'T want them, then don;t use them and the render times will be predictable and fairly fast. But you don't get blame CL because you can't render ray traced shadows from 15-20 lights with a incorrect bucket size in inder a fairly long number of minutes on consumer hardware.