Sometimes I wonder why certain people even bother with this site...
The answer isnt always 'buy modern, its great' that is missing the point entirely.
The Claud Butler mtbs from the Antaeus' era were not the best at climbing, so dont get too obsessed by its performance
A good stiff quality aluminium frame will 'climb' very well but it will feel harsh on the downs
Quality steel can be twangy going up and supple coming down but also can end up noodly depending on what frame you have
Carbon. well, it can feel great but it often lets go at a certain point just when you need it , all the fizz seems to vanish but thats my now very limited experience with older kit - try borrowing something first to see if its worth all the effort
But butt Butte no matter what - you also have to be fit