Re: 5 point harness for more than 40 lbs?
There are many more seats to choose from now than just a year ago for bigger kids, in different categories.
In the convertible category (can use rear-facing for baby, then forward-facing for toddler), there's the Britax Marathon. For a forward-facing child, the weight limit is 65 lbs. There's been some discussion of the Marathon here lately, so you may want to browse through some other topics.
In the combination seat category (can use with a harness, then convert to a belt positioning booster), there's the Safety Baby Airway. The weight limit on the harness is 50 lbs., then it can be used to 80 lbs. as a booster, I believe. I've heard that it's difficult to install with a lap-only seat belt belt and the buckle is fairly high up on the child's abdomen.
In the forward-facing only category, there's the Britax Super Elite/Husky. The Husky replaces the SE, so you may be able to find a good deal on the SE. The harness can be used to 80 lbs., but this seat does not convert to a booster. Also, it must be tethered after the child reaches 50 lbs., with tethering suggested for a child under 50 lbs. The seat is huge and you may need a seat belt extender for your vehicle to install it.
Heather