The only reason I put it on normal speed is the fire. Since it only lasts nine hours on 2X it will have been out for a couple of hours by the time I get home from work. I think I'll experiment with letting the fire go out as I much prefer 2X. If I get a few sick people that's also good practise for the doctors. The other drawback is that there's a small bonus in tech points given while the fire is alight; it is not many, though, and finding one duplicate common collectible would probably make up for it.