This website has some really great information on feeding large breed dogs and puppies, orthopedic problems that result from improper feeding and how to correct them, etc. A lot of the info on there was actually tested out and not just theories.
http://www.greatdanelady.com/
For our borzoi we alternated between Kirkland (same as diamond natural's chicken and rice) and Canidae, before Canidae changed their formula. He did really well on that. We also supplemented with a little raw beef and pork to give him extra carnitine and taurine. That is something she recommends supplementing large breed puppies with (the nutrients specifically, not necessarily through raw. That was just my choice).
Some of the research articles she links to from her site talk about how heart problems in large breeds may not actually be as genetic as people think they are. That instead they may be caused by insufficient amino acids like carnitine and taurine during crucial periods of heart muscle growth as puppies, which is caused by feeding diets that are mostly lamb or poultry protein. It made sense, and doesn't hurt to supplement to be on the safe side.