Well, i'm new to the GT40 stuff, but... if i had the money, the real thing, in my mind, is always better. With a replica you can design out all the bad atributes of the original. But isnt that what makes an original so special? Currently i have a near duplicate of a Lotus Seven, i would trade it any day for an original, just to say that this is a "real" one. But, seeing as i am not idependantly wealthy, i will settle for a replica. I think any replica built with some "correct" parts is just fine (Cobra's, GT40's, dare i say Porsche 356/550's). Any replica you can build using the proper type motor, suspension, wheels etc is close enough to the real thing that it should be recognized as something special, maybe not at the same level as the genuine article, but high up there. I cant stand replica's of any car that doesnt use something related to the original, except the body of course, like Fiero based Ferrari's or VW based MG's. I'm sure their owners take pride in what they;ve built and i applaud them for their achievements, but in my mind, they should never compare them to the original.
So, i think that the original GT40 is the better of the "two", just because its the definitive article, but for me, a replica, being the cheaper way, is right behind it. Just because i would hate myself if i were ever to own and steal from the world (by wrecking) a truly historic car.