Staying in the area of 10 reps on the big lifts gives me a nice mix of mass and strength. I'm sure it wouldn't hurt to drop the weight down a little and push for 16 or so though. I have not seen seperation or lines in awhile so I'll have to get back to you on that one.
I had seperation in my early and mid 20s but I feel it was due to my diet and low bf and cardio more than my weight training. Durring that time I got food poisoning for like 10 days. I felt horrible but looked great.