i am 100% sure i need opus 5.5 model to build stuff like this because i try lesser models because i want my tokens to go farther and lesser models simply cannot: https://fujimod.com
You don't care anyways. Actual engineering works "100%" fine with small models now. You should try it!
The best open weights models still had a lot of defects and very egregious mistakes to fix even after I provided a very well detailed Requirement/Design/ Technical Implementation plans.
Opus and Gemini 3.8 (and now Argon) did a significantly better job. So I've baseline using these two models to build this application. I now use Opus for design/review and Flash 3.8 for the code gen/implementation work.
I'm sure small models and even open big models are probably fine for many common small apps and such, but they aren't really able to perform the same across all use cases.