I had the SR80i at one point along with my AD700, so I'll try and give you impressions.
I wouldn't quite call the AD700 a "perfect opposite" for a number of reasons. First you have the bass. Bass on both of these headphones is definitely on the low side, with the AD700 still having less, yet it's very tight. And second, they both have a good midrange, with the Grado obviously having a more exaggerated one. Although, both will sound different in their own rights, but they also will sound slightly similar in their own rights as well.
A good opposite to the Grado sound is something with a "U-curve" signature. Something that is more bass heavy, dark, and a recessed midrange. A few headphones manufactures that come to mind are: Denon, Ultrasone, and Sony's XB line. There are also random headphones scattered throughout other companies as well that have the "U-curve" sound signature.
Good luck!