arc7 is an all around racket could be used in both singles and doubles, although id say it leans more to doubles. at800def is a good attacking racket for doubles.
oh, arc 7 is medium stiff and at800def is stiff so at800 def is stiffer then arc 7 and ATs are head heavy so id say at800def has more power but arc7 is more maneuverable, so more swing speed.