With the twins, they went FF F/T when they were 2.5yrs. They were in Britax DC's at the time, and Patrick was getting close to the limit. I tried rf'ing them in the 3rd row when we got DD, but it wasn't practical, so I flipped them and haven't looked back. I've tried Ricky out just for fun on occasion, and he still fits...even at 5, but I'm not one to make them ride rf'ing just because they can fit. Not at his age.
My goal with Kaylee was 3. And at 2.5yr or so I started noticing a pattern....car rides over 20min, she was puking. Every time. So when we took our trip to Cali at 2yrs and 9mo, I flipped her FF. She didn't puke. For the trip there. The trip home, she puked...ff'ing, rf'ing, it doesn't matter. So we went back to rf'ing for a few weeks and then I decided to flip her back ff'ing. She's taken a few rides here and there rf'ing, but honestly...she's at an awkward size and I'm having a hard time getting her into her seat. So, at 3yrs and 1mo, she's FF and I'm fine with it. She took, what I would assume, was her last rf'ing ride about a week ago.