even if your legs are well-developed, you should be squatting and deadlifting because
a) they are both full body compound lifts
b) they together work nearly all the muscles in your body
c) stimulating that much muscle (85% sounds a bit high but not outrageously so) releases naturally anabolic compounds that boost the rest of your body's development
You can be successful with a 2, 3 or 4-day split, depending on your experience and genetics. I've always gotten the best results from 3-day splits, so that's what I tend to recommend.