All but two of mine were done at 8 weeks/2 pounds.
Earlier is indeed better for the cat.
Less pain, faster heal time, faster recovery overall.
A lot of vet are still not on board with pediatric spay/neuter, and unfortunately, cats can and given the opportunity they do become sexually mature as young as 4-5 months.
If your vet will do the surgery, go for it, if he is a good surgical candidate, there really is no reason not to.
In lieu of a pediatric surgery, I try to get kittens done by 4 months, and no later than 5 months, by 6 months, a lot of queens have already come into heat, and a lot of toms are already spraying.