40N6 is a completely new missile, compared to the 48N6 family, and it had a long protracted development.

missile type - weight - range
5V55R - 1665kg - 75km
48N6 - 1800kg - 150km
48N6D - 1835kg - 200km
48N6DM - 1835kg - 250km
40N6 - 1893kg - 380km

Missile weight is continuously increased, and using more powerful propellant, or carbon fiber missile body, the extra gain of impulse could be much more than the weight difference would suggest.

Do not forget, that these are basically end phase guided ballistic missiles.
A quick math* of the required burnout speed for ballistic missiles reveals...
range - required speed
250km - 1400m/s
380km - 1750m/s
... and the 48N6 family could already achieve 2100m/s, so IMHO the maximum range of the system is rather limited by the fire control and target acquisition radars tracking range, than missile kinematic.


*some quick thumb rules for calculating approx. ballistic missile parameters:

Flight Times of Ballistic Missiles lofted in Maximum-Range Trajectories
FlightTime = SQRT (Range) * 14
where
FlightTime is in seconds
Range is in kilometers

Speeds of Ballistic Missiles lofted in Maximum-Range Trajectories
Speed = SQRT (Range) * 0.09
where
Speed is in km/sec
Range is in kilometers

Apogees of Ballistic Missiles lofted in Maximum-Range Trajectories
Apogee = Range * 0.25
where
Apogee is in kilometers
Range is in kilometers