you might want to try the 22 versions - they tend to be smaller, and you're likely going to get a convertible sooner rather than later. There's no way I would be lugging my baby around in the infant seat past 6 months, so I saved myself the extra weight of the 30s and went with a 22.
Yeah I had the 22 in my Nissan Sentra, which has a small backseat. FWIW I had to put the infant seat in the middle of behind the passenger seat. I'm 5'2 and have the world's shortest legs and even I couldn't drive comfortably with the infant seat behind me.
Most people I know were out of the infant seats by 8 or 9 months at the latest. I only know 1 kid who is still in it at 14 months but she's a peanut and is only like 20lbs.