So far I've only ever had four section tripods. Just picked up a ProMaster ball head and carbon fiber package that was 40% off. Couldn't pass it up. Seems to be one of those rock solid offerings from one of the little guys. Paid about $325 total.

As far as stability goes, in my experience, if you don't fully extend each section, it adds a bit more when needed. And of course, most have a hook on the center column that you can hang sand bags or a small camera bag from if things get dicey. But as stated above, the three section is inherently better in regards to stability. I've never found myself in want of more stability with my current set-up though. I think the load capacity is where you'll see the biggest difference between the two options.