Anecdotally, as someone who operates in a very large legacy codebase, I am very impressed by GPT-5's agentic abilities so far. I've given it the same tasks I've given Claude and previous iterations via the Codex CLI, and instead of getting loss due to the massive scope of the problem, it correctly identifies the large scope and breaks it down into it's correct parts and creates the correct plan and begins executing.
I am wildly impressed. I do not believe that the 0.x% increase in benchmarks tell the story of this release at all.