Interesting fact, for high levels, the free wpf we have is so good that only those well above 7WM will notice a large change.
Level 35:
7WM: 168 wpf, -2 compared to new values
8WM: 176 wpf, -8
9WM: 184 wpf, -14
10WM:192 wpf, -18
11WM:201wpf, -22
And so on. 15/30 looks intriguing for a high level because of the wpf difference. Looking at my damage calculator, the damage difference is so negligible for damage values ~30-34 compared to 18/27 that it might be worth switching to it.
Edit: Negligible compared to current 18/27 values, not new ones.