If you want my fairly unexperienced suggestion, here it is:
I can say that doing DL's and Squats on the same day is killer. Also, alternating does seem to leave a pretty big gap between Squat and DL days. Perhaps you can still alternate between them however, by doing supplemental lifts.
Wk 1: Squats and Straight legged deadlifts
Wk 2: Deadlifts and Lunges/stepups
That way you can still get the back benefit of DL's on squat day without having to worry about your legs and vice versa. It's what I would do anyway.