I'm in the same boat, limited to 40w with my Cool Fire IV, but can't go much over 25w for it to last me the day. I've mostly been playing with 28g lately, twisted and single. At the moment I'm running dual 5 wrap spaced coils in my Sapor, coming out to .6. Pretty similar to the above posted build, though I suspect the 26g build would take a bit longer to heat up.
At work, it's good enough at 25w to get me through the day, but once I get home and can plug in, it gets really nice at 30w+. Vapor and flavor really kick in then. Not big cloud chasing vapor production but quite good. Like a decent hookah pull.
Single twisted builds have been nice too, but even with one side taped off, I don't think that the airflow of the Sapor plays well in that configuration. Dual twisted have given me the same problem as 24g, that it vapes nicely, but takes ages to heat up at wattages that the device can sustain for a day's use.
Anyway, I'm also interested in good builds for lower wattages and will be watching.