The 5 series is a larger car, fabulous on the highway. Many of them share the same engines with the 3 series, except for the v8s. My wife had a 525i. really nice. Sun messed up the interior (doors). I had to redo the a/c on her 91 model, otherwise very little. You cant ignore them like Toyotas. I find they need tlc like Volvos.
I prefer the nippy character of the 3 series but the 5 series is not to be sneezed at. They are well built! They have gm trannies too, not zf like the 3.

Steve