You should know that the "real" rear-facing height limitation is where the top of your child's head is in relation to the top of the seat shell. She needs 1" of shell above her head; regardless of her height (well, length ;-), that's when she outgrows the seat. For some kids, that will happen BEFORE 29"; for others, it will happen later... it just depends on the length of her torso in relation to her overall height.
So she may have more time than you think (OTOH, she may be outgrown ALREADY! Eeek!) The weight limit at least is an absolute.
Personally, my favorite convertibles are the Britax Marathon and Boulevard. Disclaimer: I've not yet owned a Boulevard, but I'll be replacing our current Marathon with one when it expires (unless something better has come along by then; we've got 19 months to go). I like the additional side-impact protection, as well as the infinite side-adjust harness (no rethreading, no need to uninstall to change the height, and you can always put it exactly where it needs to go). But if the money was going to make a big difference to me (since the Boulevard is a bit more expensive), I'd be satisfied with another Marathon no problem.