I had a true Perc sitting around looking very lonely, so yesterday I was at a LFS, and noticed a very feisty specimen that looked to be the same size as mine. I took a chance, and bought it. I then moved mine to another tank, and introduced the new one. For a few minutes it looked as if war would break out, but then they seemed overjoyed with each other's company. They became quite rambunctious, and broke some digitata. Today they are happily swimming in each other's company.
I would never recommend keeping a single Ocealaris, or true Percula. They appear to pine for company.