I normally use a 150mm. As long as it covers the 65mm negative it is only a practical question of distance between paper and negative. I would say that 80mm or longer will work fine (as long as you can get the required distance between negative and paper).
I use a 90mm F4 Apo Rodagon and it is pretty much perfect for the format. Since it is panoramic 35mm, negative flatness can sometimes be an issue so I just use a mask on a 6x6 ANR glass carrier.