this video that shows the difference of the two seats during an impact (don't worry - it's just a crash-test-dummy).
When we bought our seat, we decided to get one with an extended rear-facing weight limit. According to national averages, he should have been fine rear-facing until he was about 3 (or even possibly 4) years old. Would you believe that he's only a few pounds away from the limit? We had to turn him around, but we're proud that we kept him rear-facing for so long. Truly, he didn't mind the way things were. He may have looked a bit squished in there, but really, he was quite comfortable with his legs bent and cuddled up a bit. It gave him a little space to run his cars along the edge of the carseat, and a nice cozy place to nap on the way to Grandma Carol's.
He's not a baby anymore, that's for sure. This little guy turns two years old in about a week, can you believe it?