Its strange seeing the Aus open play faster than the usopen. Pretty sure its a ball selection issue, b/c the surface is still fast, it just seems like you have to club the ball to see any pace generated.
As far as Zverev/Kyrgios, well there is nothing much to say. I can't get any read on them from one tourney to the next. Kyrgios gives me mental vibes similar to younger Murray (in fact I feel like he plays sorta like a mix between Murray and Tsonga), whereas Zverev seems to have issues with grinding. Both are correctible issues, and their talent is of course clearly there.