Well, in order to accurately assess and compare data from a manufacturer 3 things stand out to me .Modern 45 colt and 454 are pretty close to each other these days. Garrett is making a monster 45 colt loading that's something like 400 grains at about 1300 fps if im remembering correctly. I wouldn't feel under gunned with that at all.
1.The length of the barrel they tested in for each load.
2.The type of barrel test barrel vs regular actual revolver.
3.The temperature at time of testing.
All 3 of these can have significant impact on the fps.
Longer barrels will run faster, test barrels will run faster ,higher Temps at time of test will make it run faster.
I have a 300 gr. Load for my .460 that uses 40 grains of powder. It is of course a smack em' down hunting load.
This load is hot enough that in warmer temps during the summer while practicing it runs faster recoils sharper etc..
I think all the data shown tells me these 3 factors have to be looked at concerning the factory advertised data.
My load runs 1850 originally out of a 7.5" but I shoot it from a 10" I know I am gaining fps.
Other things to consider.
Cylinder gap also.