Would say that express pace is 90+. Anything below that is still manageable and you feel like you have some time to still adjust should something nasty come your way. There is a massive difference in pace when facing between 140kph and 145kph.
Faced some quickish guys like Simon Jones, Zondeki, Ntini, Franklin Rose etc who were clocking it at 90+ at the time and I found that a trigger came in handy just to get the feet moving against these guys. Remember at that pace you have about 0.4-0.5s to react. That's to pick up line and length, get the head and feet into position and finally bring hands into play to get the ball where you want it to go.
As long as you trigger early enough so your head is still at delivery you should be fine.