I propose a new missile exclusive to the 24 and 45 (and any other future 5th gen that will be in the game) that overall is meant to be a slightly superior without outclassing the other missiles.
Here are the differences from the 120D:
-different engine
-more advanced seeker
-slightly less drag (both front drag and side drag/lift)
Explanaition for each of them:
Different engine:
The current aim120D has a main thruster and a sustainer. The aim 260 instead would have two thrusters, one that activates at the start and one that activates a certain amount of time before impact (or when the target is getting away faster than the missile is getting to the target). They would overall have the same amount of thrust stored (same amount as the 120D), however this setup would change how the speed over time graph looks like for the flight of the missile and would ensure the missile is at high speed during pitbull.
More advanced seeker:
The seeker would have the same CM resistance, same power, all of that the same, but it would drop lock for a second, then relock the enemy when pitbulled and far enough away. This would confuse the enemy on what the missile is doing, while still allowing the missile to guide in onto the target (while this seems like a downside, since the missile cant track and whatnot, if the logic is done right, this would not affect the tracking of the missile but would only confuse the enemy)
Slightly less drag:
This would be to slightly compensate for the lack of a sustainer, and since the aim260 has less fins, it would also have less drag from the side (or less lift from the wings)