I would like to buy the canon 500 f4 but... considering the fact that the lens was built in 1999 and some rumors are saying next year a new version will come I am a bit hesitant.
can you give me any advice; in Italy the price is 6200 euro.
I've heard the rumors. I've also heard that a new 500 would be significantly more expensive (I'm sure Canon is thinking why not charge what Nikon charges for a newly redesigned 500). The current 500 is an excellent lens at a very good price. A couple of extra stops of IS would not make me want to run out and buy a new one. As a bird photographer I need speed, not the ability to shoot a subject at 1/20 sec. At slow shutter speeds you may eliminate camera shake with better IS but unfortunately not subject movement.
You could always wait until there is a new lens. But that could mean you will have to wait for several years.
Maybe there will be a new 4/500 soon. Maybe it will be a 4/200-500 but who knows.
I bought the 4/500 a year ago and I absolutely love it. Very, very sharp. Very fast AF and a good price (I paid 5.700 Euros).
I too think that a future model will be a lot more expensive. It definitely won't be cheaper.
If you want and need a 4/500 now just get one. You won't regret it. And if Canon really comes up with a 4/200-500 (probably for at least 8.000 Euros) you can always sell the 4/500. Prices for those lenses don't drop as fast as prices for DSLRs.
Make sure you get a very good tripod and tripod head.