There's a big vlamingi (still not adult yet) in the display of a lfs that's roughly 700g 10x3x3. I personally think its cramped and needs a bigger tank, and he still has some growing to do. I think a 10ft tank will be better then 99% of the tanks these fish end up in, and if your planning on upgrading, all the better. Also an orange shoulder tang will get almost as big as the naso tangs. I think you still have plenty of room left in your tank, its 10ft long plus its an L so you have additional length.