LO1 is nearly 2.5 and averages around 32 lbs. We have two britax marathon 70 g3s currently rear facing in each of our cars, but I definitely think he is about 1 inch from the top of the shell. From what I understand, the marathon's directions say to turn forward facing once your child reaches 1 inch from shell (unlike the chicco nextfit or graco 4 ever which is 1 inch from the top of the extendable headrest).

So, would you buy a new car seat (I'm thinking the chicco nextfit) in order to extend rear facing a tad longer?

The nextfit also has the benefit of more side impact protection (which will be helpful forward facing as well). I am due with LO2 any day so I'm sure the Britax marathons would get good use from him as well once he outgrows the infant seat, and they've been used by LO1 for almost 2 years since we switched him from an infant seat early.