Adding it to each element one at a time vs adding it to 50 at once makes no difference after the event is bound. You may be able to do a jsperf to prove that doing one or the other binds the events faster, but the actual handling of the events will not be any different assuming that in both cases you are binding directly to the elements and not doing delegation.
On the other hand, using event delegation such as binding a click event on the body and testing if the event.target matches a selector will be slower than binding the click event directly to the element because the event will have to bubble up to the body before it can be handled. It will also have to execute all handlers that happen before it, so that can impact the performance too. That's why when using event delegation it's best to set the delegate target as close to the event target as possible.