You may be able to support a high bioload but I would be more worried about space within the tank for the fish themselves, jam a lot in there and you are bound to have compatibility issues (even with your really clean water). As for the tang issue some will say that a powder blue needs more swimming space then what a 90 can give but its really a matter of opinion (some would probably even say the same in regards to the sailfin), another issue with powder blues is they are notorious for getting sick early. At the same time know many people who have had multiple tangs in 50-60 gallon tanks and the tangs seemed happy/healthy
With all that said I am probably not the best person to give advice on fish b/c I use to be known for having quite a few myself and pushing the bar.