My Sagnol mare Silhouette has very long legs (especially from a short legged dam!) and super movement. She was Gold Premium with the RPSI and scored 8.2 on her movement. She has nice suspension, an awesome balanced/uphill canter and gorgeous both inside and out.
Yes, depends on the mare of course, but I have to say that both of my Quaterback's got way more suspension and elasticity than their dam. Both are very leggy, but she has a good length of forearm as well.
The Sir Donnerhall's seem to often inheret their fathers long legs, elegant type and really floaty movement.
Looking for stallions for the upper levels of dressage.
Remember that lifting and carrying power begins in the hindend. While today's very fashionable long legged horses look more elegant, they can sometimes (often?) be a bit light in the hindquarters. This affects their ability to take more weight behind (i.e., their "sit" ability). IMHO, it is therefore far more important for upper levels to have a horse with a very good engine (and a very trainable mind certainly doesn't hurt, either!).
It's very rarely the suuuuuper long legged, suspensions, suspension, suspension horses that make the upper levels in dressage. They make the auctions and Bundeschampionat ;-) Gross generalization, but there's really very little Sandro in international dressage.
Try Hanoverian and Oldenburg D-line derivatives along with the Boldero-group, Rubinstein/Rohdiamant group or in more limited capacity, the Westfalian F for excellent dressage potential and VERY good canter work (!). And definitely the Kostolany bunch from Trakehners and KWPN. Solid, proven time and again, upper level success galore.