Don't get me wrong, I'm not a big fan of E60's and given a straight choice I'll take the E39 any day of the week, but at that price point...
I know it's a silly comparison but the reason I mention an E60 (and not an F10 that are also available at around the $40k mark) is that there's a much wider choice of V8's out there, both older and modern, whilst an NA V10 is much more of a unique proposition and likely one of the last mass-market ones ever made.
If I had to spend $60k on a super sedan I'd take the best E60 out there at $40k and have $20k left over in a maintenance fund, or hell... throw it at a manual conversion before I spend it all on a lazily presented E39.