Ds is currently rf in a Radian xtsl. He just turned 5, he's about 42 inches tall, and is about 42 pounds. I'm keeping a close eye on his weight so that I can turn him when it's necessary, but when I look at the harness slots, his shoulders now are just barely below the top harness slot. Since a ff harness is supposed to be threaded through slots above his shoulders, I'm wondering if this means it's going to be time for me to find a new seat? I swear I've seen pictures of 7 year olds in the Radian, but obviously, I can't tell from a picture what size the child is actually.
If I do need a new seat, I would be considering a Britax combination, I think they have on with the anti-sub clip? Is it likely a Britax would last longer in terms of harness height/overall booster capacity? Or am I just thinking of this all wrong?
I'm not entirely sure about your Radian, other than I know kids can gain/lose some height once installed more upright or forward facing. As for the Britax combo, it's the Frontier 85 and it doesn't have the anti-submarine clip because it has the harness. Once used as a booster, you CAN buy the clip and use it then. The Parkway SGL(I think) comes with the clip, but it is a dedicated booster. The Frontier has the highest top harness slots out there. I believe they are 20", which is 2-3" taller than the Radian, I think. We have the Frontier and love it. It is big, much wider than the Radian you are used to, but my DD finds it comfortable. She is 41lbs and 40.5" tall. Anyway, just wanted to say we have and love the Frontier.
Diono allows you to continue to use the Radian with the shoulders exceeding the topmost harness slot as long as the ears are within the shell of the seat and the max stated height limit is not exceeded (and, obviously, weight limit.)