>>28496666 (OP)>checkedYou're nearly on the money, an E55 with a 5.4L supercharged M113K making nearly 500hp while looking like grandpa's Mercedes sedan is a great choice if horsepower and speed are metrics you want. Price, even, since they're rather affordable for the performance they offer. A similar S55 works too if you want the same thing in XL size, price is usually the same.
If you don't care about 0-60 or 1/4 mile times, the land yacht is what you want. An old Continental like
>>28496668 , or an old Eldorado with the 500ci (8.2L) V8. Maybe even an Imperial Lebaron with a 440ci V8. If you don't want something decades old, don't care about speed/tech, and just want "an old man's car with a bit of class and a big engine" then the last answer I'd say is a late model Lincoln Town Car.