Here are the results of my uptime tests.
Opportunity Strikes (Regular NOT Superior) and Sentinel's Ward are slotted in Screech, and I have 2 LotG slotted.
On Excelsior: spamming all my attacks, with a few useful OS procs and a few wasted, got me 8 uses of Vulnerability in 4:45.
Page 4 Uptime: 42%
On Brainstorm: with Screech on auto, no wasted procs of course, I hit Vulnerability 12 times in 5:00.
Page 5 Uptime: 60%