This is solely based on my personal experience:
- My I-751 was still being adjudicated at the time when I filed N400 under 3 year rule so they had all the evidence already
- I submitted only the bare minimum for N400 (marriage certificate, taxes short 1 year bc it wasn't available yet, and that's all)
Naturalized much sooner than if I had waited for 2 additional years. And, again, didn't need to collect/submit any additional evidence so it wasn't a hassle at all.