I demoed the new Blades and currently play with the Pro Open.
The 18x20 was 4 grams heavier on the scale than the 16x19. It was also a little less head light. Overall, I liked the 16x19 better. In my experience the 16x19 is more lively and I got better feedback from the ball with it. I felt like the ball was on the strings for a lot longer. The 18x20 felt great too but I found it hard to keep balls deep when I was on defense.
I have 2 16x19's coming straight from Wilson. I'll report back regarding their weights. My Pro Opens weighed 319 and 327 strung with the same string and same over grip.