best carseat for a tall child

my son is 30 months old, 35 pounds, and already 40 inches. He is outgrowing his roundabout and I'm not sure which carseat to buy next. I tried out the marathon at a nearby store, and he seems to have only about two inches until his shoulders are over the top harness slot. At 49 inches it seems like he would be way over the slots. I would like to keep him in a 5 point harness for at least another year. Any suggestions?

Britax Husky. DD has never complained. It's big and was hard to install the first time but I really like it.

Ditto the Husky
http://www.car-seat.org/showthread.php?s=&threadid=553

My dd turned 3 in June, is 40 inches and 36 pounds--that's 100th percentile for height, PLUS she's long torsoed, so she fits carseats really strangely. She outgrew her Alpha Omega by height at 2 1/2 and 37.5 inches tall. We tried out the MA and the Husky, but she was already pretty much even with the third slot, and I didn't think she had enough growing room. In fact, it sounds like she fit the seat much like your 2 1/2 year old does now, heightwise. I would DEFINITELY get the Husky in your case. It is a big seat, and heavy, but I have always gotten it installed in 10 minutes or less...now that I'm good at it, it takes me about 3 minutes, no kidding! In a small sedan (I have a four door 1991 Honda Accord) it takes up enough room that it's uncomfortable to sit on either side of it for very long. Since we don't have other kids, it works for us. We could put her outboard and have plenty of room for another carseat or passenger, though.

Here's some pictures of dd when we first got her the Husky, she was 31-32 months old then, I believe.

http://photobucket.com/albums/0603/scatterbunny/Britax Husky/

These were a few months ago
http://photobucket.com/albums/0603/scatterbunny/Husky in 1991 Honda Accord/

Like I said, now she's moved up to the next set of slots, at 40 inches. She'd be inching very close to the top slot of the MA, I'm afraid. I think she'd still get a year or so out of a MA, but not nearly long enough, IMO.