I'd go with the 4/5 blank. But then again, rod builders are using the 4/5w designation as a starting point. I've found most rods will throw 3 line weights. A lot also depends on the lines being used (brand wise).
If in doubt, get both blanks.
I just got Joni and I some T.L. Johnson Synergy blanks. I got a 8' 5w for me and a 4/5 7'6" for her. Glass rods with graphite in the butt section. Faster than Diamondglas but slower than a WT.