What percentile is she in for weight? Does she carry her height in her torso or her legs?
We bought the First Years TrueFit at kids.woot.com for $99 when they were having a sale. I love the seat overall, but it's not really a great seat for tall kids. The top harness slot isn't that high, so DD1 outgrew it ffing by 4 years. She is >99th for height, 75th for weight, and has a long torso. It rear faces to 35 lbs, so it's not a bad extended rfing seat if you have a tall, thinner child; I just don't think it lasts long enough ffing. (The stats say the top harness slot is 17.5", but I measure it as 16.5-17". She outgrew it at the same time as the Marathon, which is listed as a 16" top harness slot.)
We have a Radian. It's a good seat, but it can be hard to install. Rfing weight limit is 40-45 lbs depending on the model. Top harness slot is about 17.5".
The seat I'm currently waiting to buy is the Graco My Size/Size4Me. I have two expired seats to trade in at BRU when their sale starts. According to the specs, it should rear face DD2 to almost 4 years (40 lb rfing limit with adjustable headrest). Top harness slot is between 17.5-18", which should last us until at least 5 years. I'm hoping Graco has the harness issue fixed, because I think it's an ideal seat for tall kids.