My list of equipment, assuming you're not wearing floppy clothes:
1. Tires first of all since it's the cheapest most effective improvement at all speeds, depending on what you start with
2. Wheels. Can save even more weight than tires, most inexpensive improvement after tires, and some rim shapes really do produce gains.
Clipless are way down my list because they'll help on sprints and "feel" but objectively not much else. You might need them if the other group roadies make fun of you.
edit: I forgot 3. Tubes, because I don't bother with getting better tubes. But objectively high end butyl tubes can save some weight and rolling resistance.
CF bike isn't even on my list for "huge gains" or even medium size gains from entry level aluminum to mid-level CF bike. I'd agree that some small gain might be had from upgrading entry level to mid range, but mostly from saving a few pounds.
Last edited by wphamilton; 11-20-19 at 01:20 PM.