Overcap Feeders specification should start with the real closure.
Overcaps and protective covers can be light, flexible and prone to nesting. Feeder design should consider static, stacking, deformation and how the cap is pressed or placed onto the product.
For a better buying decision, the useful comparison is not only hopper size or headline speed. It is how the feeder behaves with your closure, how the capper receives the cap and how easy the line is to run after changeover.
The safest specification route is to start with real closures, target output, line photos and the exact point where the cap must be presented. That avoids choosing a feeder on a generic speed figure that does not match the cap or capper.