There are multiple variables, that effect the advantage of going to a roller.
Duration, lift, tappet diameter, base circle diameter, available spring rates, Engine RPM.
You can't just say, the advantage will be bigger, with more duration.
If you look at the flat tappet restrictor plate cams we ran in NASCAR a few years ago(mid 250's at .050"), because of the 2.37:1 rockers, limited RPM, ultra-light valvetrain, there would have been zero advantage going to a roller.