Well, I'll have to tease you a little bit... I just so happened to have recently had a Savage 11, chambered in .270WSM and it just so happens that the only factory ammo that it ever shot was 150gr Winchester and it just so happens that I did, indeed, fire that ammo over a chronograph and it just so happens, that I have no recollection of the speed.
Anyway, it won't matter much. Unless someone else's chamber was cut with the same reamer as yours, the speeds won't have much relation.
Most factory ammo doesn't reach published specs, the particular exceptions I've found are 17HMR and 7mm-08, for whatever reason.