"...the No. 4 has an a bit shorter barrel..." Should be 25". A P-14's was 26" with a 1 in 10 LH twist. Mind you, it was designed to use the .276 Enfield, not the .303.
Keep in mind that the Pattern 14 was intended to use Mk VII ammo with its 174 grain bullet at 2440 FPS. Typical 180 grain loads run a couple hundred FPS less. Said typical loads have been killing big moose here since the 1920's or so.
Rummage around here. There's lots of load data. 303british.com