The great carseat extravaganza...

Mr Britton is now 17 lbs- which means that combined with his infant carseat, carrying him means lugging around 30+ lbs. I can't do it anymore (I'm a weenie) so we've been shopping around for a convertible seat that stays in the car. We've narrowed it down to a Britax- they are made in the USA (WOO HOO!) and have the highest safety ratings of all the carseats. They are also the most expensive, but we're willing to spend a little more to ensure that Britton is safe. One of our choices can hold a child up to 40 lbs and the other up to 65... The 65 pounder is more expensive but it will last longer, but will he really want to be in a carseat when he's 5 or 6? Does he really need to be? And what if by some crazy chance (haha) by then we have another baby who will be in need of a carseat? And what about colors? The interior of my car is gray (kind of yuck) but the seat cover I like best is tan with little brown swirls. If you know me at all you'll know what a problem this poses for me-- as I am OCD about things matching! But I won't always have that car, so... Thus my confusion. I have spent weeks now reading reviews and blogs about it, but if anyone has experienced this kind of nightmare, please share your thoughts as I am about to go crazy.