Truth is it probably makes no difference which way you start, I accept that. But for me, I find it easier to get the contrast "right" going with grade 5 first. I can see the blacks coming up and I usually select the point just before the blacks go solid. Its kinda like, "ok thats the contrast fixed, now lets get the exposure right".
Its also very useful to be able to burn in a cloudy sky with grade 5 to give a bit of definition to edges, and as you say, control the mid tones by dodging etc.
I saw a good article in Photo techniques some time back where a print was made ("scientifically") by both split and normal grade printing and tones over the print then measured. It did indeed prove that single grades will do anything that split grade does. I still find it easier to split grade though!!