My feeling is that you'd obviously prefer to have two highly talented 7 footers in your front court, but talent, ability, and productive are the most important factors.
I'd rather have two All-Star caliber guys who are 6'9-6'10'' instead of playing a stiff or two in the frontcourt just for the sake of having size / length out there.
Height is also pretty overrated. Standing reach and general ability to use one's size matters most. Elton Brand is a very effective defender at the 5 even though he's 6'9''. Ben Wallace was an All-World defender despite being 6'10''. Glen Davis has been a much more effective defender in his career than you might expect, because he's learned how to use his size and also take a fair number of charges. Chris Kaman is a pretty poor defender even though he's a legit 7 feet. Javale McGee has never been able to translate his awesome measurables into productivity that helps win basketball games.
Intelligence, instincts, skill, energy, and desire can make up for a lack of a couple of inches.
All the same, a team that can field seven footers with All-Star talent is going to have the advantage, but there just aren't many of those guys around.