Outbox model is not only for sending notes. It's about using the outbox you want to keep your notes, the inbox to receive notifications in your relays and using everybody else's outbox setting to download their posts, regardless on which relays they use. That's the outbox model.

There must be something else causing the lack of smoothness for you. This version is almost 2x smoother than the previous one. The relays themselves use less than 1% of the processing power, so it must be something else.

Is it just the jumping of items on the screen? Are the images loading fast or are they also slow?