....I think the 745i would be the best bet. With any old 7-series, you're going to be spending lots of money on upkeep, after all, these aren't plain old workhorse Mercedes diesels here (one of which I do indeed own, and use every day). I have an '84 745i and while I only use it in the summer, I have a total blast driving it. Sure, it's no handling miracle but having a big car that will effortlessly cruise the interstates loaded to the gills with family and luggage and one will dust many performance coupes at that is a very cool thing. It's the whole "sleeper" appearance that got me. Sure, about any German automobile can spend hours on the freeway cruising at high speed (i.e. MB S-Class, BMW 7-series, Audi A8, etc..) but having a somewhat rare bird like the 745i makes it all worthwhile. I used to own a Mercedes 6.9 which I used on nice days but insurance and upkeep was phenominal compared even to the Bimmer, which is why I opted for a BMW with a turbo six over another big Mercedes with a honkin' V8. So, case in point, if you're going to spend your hard earned dollars on an interstate cruiser, particularly a BMW, hold steady and find a nice 745i. You'll be glad you did.