What?? Not sure I understand. You introduce more than one variable and then ask if they matter...
Roll crimps will GENERALLY produce lower pressures. Pressure and velocity are not necessarily related nor correlate. Velocity is a function of powder burn, and if it burns all at once you get a lot of pressure. If it burns a little slower then you don't, but you get the same velocity (all generalizations here so please...). Fast burning powders are good for lead and other compressible shot. So not steel which must have a slower burn. Wads change pressure. Primers change pressure. Hulls change pressure. Crimps change pressure. Powder changes pressure.... There is a lot of data on various wads.
If you wanna roll crimp trap loads... why? No need. If you wanna roll crimp hunting loads there are many good reasons to, but few "well you gotta because" reasons to. If you have a specific wad/hull question post it.
