With an engine fire, certainly descend as quickly as possible. Max drag configuration (Gear down, Full Flap), and set airspeed for Vfe.
Certainly a sideslip would increase ROD and so would steep turns. Depends where your landing target is, but if it's 2,000 feet vertically below, then I would use steep turns to descend at Vfe above target, and sideslip in on a high final approach.
Your call really.
Just smoke....? Well PIC has to make the decision whether he has a fire or not. If not a fire, then the drills are aimed at a possible restart and to maximise your time in the air to glide to that ideal piece of tarmac. If you decide you have the time to glide, then you would be in a Minimum Drag configuration (Gear retracted, Flaps up, Cowl flaps closed etc), and select the attitude for Vg.
But again it is very much your call whether you treat smoke as an engine fire, as it may very well turn into one if it isn't already. On the other hand, if you'd had a fire and the shutdown drills were completed successfully, then while you are descending like a brick it may well be that the fire goes out, leaving just some smoke! If so, then certainly consider changing configuration back from max descent to best glide, and re-evaluate your options.
The checklists only tell you what to do once your decisions have been made. They don't tell you how to make decisions, or how to re-evaluate your decisions as things develop.