R.W.
Graco just came out with a new seat that has an extended 5 point harness limit (65 lbs). I bought one at Walmart for about 150. Here is the link to the seat on the Graco website.
http://www.gracobaby.com/catalog/product.aspx?modelNumber...
The Radian and Britax seats are good too, but pricey. You have to be careful with a child this size. Many car seats advertise a high weight limit, but that is only for use as a booster. You have to shop carefully to get an extended 5 point harness weight limit.