The standard AR start drop off is 50m. 50m in-game is still relatively "close". I would like to propose AR getting bumped up to 75m like the F2000.
The battle rifles (Scar/fal/AK15) with AUG/SG550 are still 150m.
Maybe AR guns that are meant for CQC can keep 50m start drop off? Not sure, I would think guns like ak5c or hk419 fits CQC and some mid range for ak5c. Just a thought, but 75m range is fine too.
SMG/PDW effectiveness sharply declined by ~50-60m. For MP5 @ 50m, it does 25 dmg with a 800 RoF. UMP @ 70m does 25 dmg. They are still decent damage, which is fine.
This 75m drop off for AR helps them compete with SMG before their effective zone.