Achilles love to swim constantly, they need the room and high flow so they can stay active
How bout a chevron...they are very hardy and not hit and miss like the powder family at all...
Have you looked at a Red Sea Sailfin? Also the juvenile Atlantic blue tang has a very nice complement to the coloration of the purple tang. They go from yellow with a nice blue rim to being all blue with a lined pattern similar to that of the purple tang. They're also cheap.
Yes Achilles do need more room then another tang that is the same size. Achilles really swim a lot
One of my favourites even though I don't currently have one is the powder brown tang, or one that I do have with my purple is the yellow eye kole