I have a Pontiac Torrent. They don't make Pontiacs anymore, but the Chevy Equinox is the same vehicle. I only have two kids right now, but for a couple weeks this summer my 5-year-old niece was with us so I had to fit 3 car seats. I successfully fit in a Britax Frontier 85 (giant convertible/booster), a Radian, and a Graco. Now that I'm pregnant with #3, I'll keep that same set up. My kids will be 3, nearly 2, and newborn when this one come along, so all will definitely be in carseats for awhile.
My DH drives a Honda CRV. We currently have 2 Gracos in there and there isn't room for a third. I think I'm going to have to swap out one of the Gracos and get 2 Radians in there to make it work for 3. If for some reason we're rolling in money at the time (not likely), I'll just buy 3 Radians so they all match..lol.
To me it makes more sense to get car seats that will work with your current vehicle (if possible --- i know some are just too small for it to ever be possible), than to get a new vehicle to accomodate the gigantic seats.