I think you've described exactly what I'm experiencing in my Selle Italia Diva, too. I don't have sit bone issues, I don't have chafing, I don't get saddle sores, but man I get tender from the pressure just in front of my sit bone area after about 90 minutes. I tend to scoot forward in this saddle regardless how I have my saddle adjusted. I have about 2,500 miles total on this saddle and thought it was just me.
2010 Look 566/Selle Italia Diva Gel Flow (roadie)
2001 Cannondale H400/Terry Butterfly (haulin' the kids)
Sold my horse and started cycling. Miss her everyday, but I love my bike!