I'm not a LW hater and always argue against guys trying to convince people not to go through with adding a 60˚. But just wondering why you want a 64˚ on top of a 60˚? I ask because I know why I got my 60˚, and given my experience with it and the distances you give, I don't see why you need it. I got my 60˚ for two main reasons:
1) Too many green side shots where a stock pitch or chip landed hotter than I wanted with the 54˚. Plus I'm less comfortable relying on judging long roll out with a low chip than on hitting a higher pitch where if I land it where I want I can be more confident the ball will actually stop closer to where I want it, so 60˚ helps there too.
2) Distance gap between short game shots (say < 50 yards) and shots I'm comfortable hitting with my 54˚ or PW. 60˚ closed that gap for me.
That's all to explain my question. Your "full" 60˚ goes 70 yards, and it sounds like you're also fairly comfortable with some partial wedge shots, so it wouldn't seem like you've got any gaps between full 60˚ and green side shots. So you want the 64˚ for around the green? Do you play a lot of courses with ultra fast greens where any but the best possible miss leaves you with the choice of a miracle 60˚ shot or barely keeping a more stock pitch or chip from running off? Do you just like being able to swing more aggressively on green side shots and figure you might as well try an even higher LW? Some other reason?
Anyway, given you do want a 64˚, it depends on your game. I personally wouldn't really like having a gap in my long irons. I find partial shots with those much harder than with the wedges. So I personally wouldn't drop the 4h. If you can swing buying a whole new set of wedges, I think I'd vote for the 46/52/58/64 plan.