I believe the key to balancing logic and feeling in a speech is to carefully watch and react/adjust your message according to how you see your audience responding. It is important to do a psychological audience analysis before your speech. In other words, you should get to know/have a feeling of the feelings of your audience before you speak, but you should also be watching attentively in the moment so that you can change course or stay on the path you are on depending on the response you are getting. If you start out working mainly on feelings that may get the audiences attention and hook them but it should be supported by logic in order to let them know you are credible. You may have crossed the line if you see people becoming uninterested or suspicious of what you are saying.
I agree that it can be good to adjust your speech based on how your audience is reacting. I know that when I have listened to speeches, I enjoy when the speaker connects with my feelings, but I also appreciate when they use logic to back up their information.
I agree that reading the audience can help to create a better balance between both feelings and logic. I think it’s also a good idea to support your pathos with ethos.