That would be the speed limit on atmosphere, in space I think VF-25 should be nearly equal with VF-27 when its equipped with SUPER pack, the main problem I think is the pilot endurance to resist the stress when piloting the VF-25 to its peak performance.
My theory on newer generation of FAST pack is the engine has been compacted and it carried less fuel, so they got more room for weapons.
BTW, I forgot, but someone actually counted the number of missiles on the VF-25 SUPER pack.
It would be interesting if Mr.March put the statistic of all the FAST pack unit on a single page so we can compare one to another. I think the old Dave Deitrich site got one RPG page for all the FAST pack stat.