I supect a tad more due to the ARs gas operation...Quickload suggests that load, with a 16" barrel, will come in right at 2900fps and with a 26" barrel, velocity would be around 3240fps. A gain of roughly 350fps, or 35fps per inch of increased barrel length. That's a lot, but then again, the .223 Rem really needs more than a 16" barrel to burn all of the powder it can hold.
Incidentally, QL shows that as being a 110% compressed charge. A slightly faster powder, like H322 or IMR4198, might be in order. Both show the same velocity and higher ballistic efficiency, without being compressed so much. Particularly if you do most of your shooting with the 16" barrel, the Varget load is not ideal.