Iv hit both Dave.....
If you tend to take a generous divot the Di9's have a little more width in the sole and also launch the ball faster and higher....
They are also pretty long...They have the fatshaft in them which plays a little stiffer than flex......Regular in them would be pretty stiff standard shaft.....
The Ci9's are really nice too....A lot more sleek looking but still with heaps of forgiveness.And they are long also....I would expect you to gain a little yardage with them.....There is plenty of help in them for the high mid and low handicapper....
If your going with Wilson i would go with the Ci'9's as the better you get the more comfortable you'll feel looking down on a slightly more sleek head....But with the Ci's you'll still have the help you need for the off days.
Hope that helps 
