With a 28" bbl you don't need uber pressure to get to 3000 with 180's in the SAUM. The guys over there shoot competition, and need their guns, brass to last a while. That is the point of going to the SAUM over other fast 7s: it is easy on throats.
Barrel length does matter, and long barrels can give much higher velocity than short ones. If comp shooters need 28" to get the most out of their 308s, and 30" for 30-06, then 32" is probably closer to ideal for a 7 SAUM.
