Advantages for the 72'x280' is I can fit 12 10x14 stalls, 3 10x9 cross tie areas, and 1 14x20 tack room. There would also be a 24'x66' area in between the stall area and the 66x198 arena.
Disadvantages? Are 10x14 stalls a disadvantage?
With the 83x260 I can have 12 12x12 stalls with 14 isle ways but have only 15-20ft in between the stall area and either 4 ft of space on both sides of the arena or 8 ft on one side of the arena. I could put tack lockers along the wall separating the stalls and the arena which would take up that space.
Which would you prefer? Is a regulation dressage sized arena big enough for dressage riders on an every day basis? I have an outdoor 160x170 (that will be enlarged to 170x230.) I do want to hold clinics too.