Perhaps I should have been more specific with my question, regarding the handling, I am aware they have front suspension this will affect it, put if you pitted a top class retro xc against a top class current xc - Would any of the bikes abilties be similar?
Ahh now you are quantifying.
My modern is set up in the same do it all XC general what i did /alway done on my bikes.
Saddle height is the same as is the reach to the bars, gearing etc. And it does perform better, more stable handling ad more "performance" (easier more stable corneringsay) for less brain and body strain. It is also surprisingly comfy too, but as much as i love it (despite the Ritchey "wet look" seatpost loosing it's coating and slipping constantly after 100 miles of use) i do stilla he a glut of retro bikes i love too! (it nice to know if the weather is grotty i can hose it down and not wear about rim wear, making sure my chain si spotless and my cassette is'nt wearing too much!)
I was forced into borrowing a mates Santa Cruz 29er on a trip to Wales recently (as the pivot bearings on my full sus superlight gave up
After a days riding at Brechfa, I can honestly say that it's the best bike I've ever ridden. I've since sold my full sus and ordered a 29er hardtail
Comparing this to say my 1997 Orange Vit T is like chalk and cheese though.
The modern bike was heavier, but climbed better and would walk over the Orange downhill.
However, when I ride my retro bikes on my usual trails, I always finish with a bigger grin than when riding modern.
It simply tests your skills more, and I love riding them quicker than my friends on their modern bikes
I'd be very interested in the seatpost reflector if you decide to split.