For me, the car needs to have enough power to keep up with at least 85% of the cars on the road yet it should be fun to drive too.
High HP and low TQ is always a struggle and not so fun to drive. My current daily is a 2002 E55 with 350 HP/400 TQ and I can keep up with most of what's out there.
I also have a '12 X5M and at 620/570
, I am very pleased with that too.