Clek Foonf (it's not out yet though), Diono Radian, and Graco MyRide/Size4Me are all good seats for tall kids. Generally speaking Britax seats aren't great for tall kids because the shell is short so it is more quickly outgrown than other seats. For a tall baby, I would skip that brand all together. I am sure Penguin can jump in here and help out with some other possibilities because her kids are really tall too!
I like this lady's reviews and below is her recommended list.
For the record, I have the Peg convertible but my daughter is on the smaller side and her torso is short. I think in your case for a tall child and long lasting seat, I would try the Radian or one of the Graco's. If you can wait a few months, you could try to get a Foonf or the new Chicco Nextfit which come out next year.