carseat or booster for 4 yr. old?

[freedom]

DS will turn 4 in about a month. He is about 34 pounds, 39 1/2 inches right now I think.
He's in a roundabout most of the time, and in my parents car a titan. He's already outgrowing the titan...and is very close to outgrowing the roundabout.
We have a Dodge Caravan-not the grand caravan-just the regular-so there isn't a lot of room.
What are the best booster seats and car seats for a 4 yr. old, and that fit in a smaller mini-van?

[JBaxter]

Look at the sunsine radian at albeebaby.com. It is a narrow seat tha goes to 49in and 65lbs. 179.00

[freedom]

Thanks!
Do you think the height/weight limits are realistic on the radian? (I've heard some of the height limits on other seats didn't work as long as they said they would)

[Scatterbunny]

Most seats are outgrown by height before weight, that's just how it is. :)

My dd outgrew the Alpha Omega/3-in-1 at 38 inches tall, even though the height limit is 40 inches.

She was too tall for a Britax Marathon at 46 inches tall, even though the height limit is 49 inches tall.

The Radian allows an extra 6-12 months for most kids over the Marathon.

At his age, height and weight I'd most definitely keep him harnessed, though.