This article is important basic reading: http://drsquat.com/content/knowledge-ba ... ning-split
This article was pretty good when it was written (2007). http://www.bodybuildingweb.net/blog/bes ... le-growth/
This one written in 2010 came to the same conclusion. http://www.simplyshredded.com/strong-sc ... sults.html
Regardless of what the study found to be optimal, no single rep range, total number of sets or training frequency will give you optimal results forever. You need to mix it up and change these variables from time to time. You are an individual and should train like one.
This article (with references) says that as long as you get over 60% load, your good. http://www.exercisebiology.com/index.ph ... le_growth/
Here's a good debate on last year's controversial 30% is as good as 90% study. Lots of good links and good analysis. http://www.leangains.com/2010/08/high-r ... -gain.html
My summary of all this is to vary your rep ranges. Include light and heavy days. Put some effort into. Don't just go in, do the reps and leave. Take each set to the point where form starts to break down and stop. You need to reach the point where it's hard to do the last rep but not so hard that you can't do it. I don't see the point in going past 20 reps or so but personally, my lower body has more stamina, so on light (60%) leg presses, I could get up there.