I've been able to find SAC data for the P-51H that gives weights, power/supercharger boost ratings and such for various configurations (standard combat, interceptor, ferrying, etc) at World War II aircraft performance, but not for the B/D, at least for later in the war when 75-80" was approved (the H data had ratings for 80" and 90", 90" with ADI).
But from said data, the P-51H in interceptor trim weighed as low as 8450 lbs take off. Also, drgondog has made mention of P-51D at 67" on half fuel and set up as an interceptor (8900 lbs TO weight) getting 452 mph at I believe about 22,000 ft and a 4200+ fpm initial climb rate.
But I'm not necessarily talking weight here (the XP-51F/G could weigh between 7200 and 7900 lbs depending on set up when tested). I'm asking more about aero tweaks and differences between the models, since aero played a much bigger role in top speed for the same power outputs. Weight does however govern climb rate for a given power output.