I have zero interest in the F40. Does nothing for me at all.
The F50 is a superior car in every single way: V12 over V8, NA over turbo, and the roof comes off. Perhaps not quite as well designed externally, but otherwise it's not even close.
Offer me an F40 or a 959, and I'd take the F40 though! I'd probably take a common or garden 458 over an F40, truth be told.