Can't say about fighter aeroplanes, but the DC-6B's handling was improved considerably over that of the original DC-6.
Even the TAS (same weight and cruise BMEP) was increased slightly by the longer fuselage.
And then we come to the original B707's.
The original short body machines were a real handful, especially during takeoff and landing. Higher cruise altitudes were a problem as well.
With the later long body machines, handling was vastly improved, not just by the longer fuselage, but by the taller vertical fin...and much improved yaw damper.