Depends on the lift. A higher rocker arm ratio won't change the advertised duration much, but it can easily double or triple the duration at the higher valve lifts. Of course, those events happen very, very quickly so it might not have much effect on power.
On my 511 race engine I would pick up about 10 hp from 1.85 rockers on the intake rather than the usual 1.80 rockers. The 1.80 rockers picked up a bunch of power from 1.50 rockers. My 470 pump gas engine didn't pick up power from 1.50 to 1.70. I ended up using the 1.65 T&D rockers on that engine since they were the nicest rockers but they didn't add any power over the cheapest set of 1.50 rockers that I tried.