I think that the diesel burning pistons will offer best performance / economy over a "cheap" TP and provide the ideal stop gap for the "moderately wealthy" pilot (as opposed to the super rich). For example a DA42NG will be far cheaper to buy, maintain and operate than the E500, will burn half the fuel and will cruise only slightly slower at similar levels with equal if not better range, and has two engines.
If one can afford mega bucks then I'd go for something that can cruise at 250-300kts, ideally a Phenom VLJ.
Under a million dollars will buy a used B200 King Air which has all the capability one needs....good load carrying, good range, good for the higher flight levels, reasonably quick, great avionics and reasonable times left on the engines. Add another quater of a mill and you can have zero timed engines with 3600 hrs left on them. Of course you get a KA maintenance bill to go with it...