I agree with the two machine option. Also you may want to look at providing plumbing so that you can run two machines through one gun when you have only one operator. I got some feedback on this concept a couple of weeks ago on this or another bb. Basically run outlet from two unloaders to the inlet(s) of a third unloader, outlet to gun. A 21 gpm/4000 psi should work nicely.
This would give you advantages stated above, plus one set of spare parts would serve as back up for two machines, not one.
I also clean brick. I think the high gpm concept should work well for the pre-rinse and post rinse, but I think it would beat me to death during the PWing.