I have read up on some of this before and this is a question that may have no black or white answer. I say that cause the metabolism of snakes can vary from individual to individual.
With that said....I don't speed feed. My snakes get one meal a week, and a lot of my adults get one meal every other week. I have noticed normal growth from doing this, or what I consider normal growth. Let's use my male northern pine Solomon as an example.
Solomon was born in 2001. I fed him one meal once a week. He grew from being a 17 inch baby to being 4 1/2 - 5 feet currently, making him 3 years old. He is now big enough to breed. If he was a female, I would wait another year for some more girth to arrive, as northerns lay very big eggs.
Overall, his metabolism seems normal, he is lean, never fat, and never has fat rolls. Some of my other snakes unfortunately, developed fat rolls, and that was with one meal a week! When they tend to lay around in cages, they can still get fat! So, I had to play it by ear, feeding every other week here and there, until their weight was managed.
I have noticed substantial growth in all my other snakes from once a week feedings. The question is, should they get more than that? I personally don't think that twice a week during the first two years is bad, since they do grow fast in those years. But you still need to watch for fat buildup.
I saw on one breeder's webpage the explanations for why power feeding is ok and should be acceptable. Funny thing was....every pic of every snake showed a fat snake! Breeding at 18 months.........is that really good for them? Remember...egg laying can take a lot out of a female. If they are the correct size...it is possible and does happen..but is it really good? The opinions of course would waiver. I personally think that females should be given at least 3 years.
I do think that snakes that don't have weight problems and were not sped fed may tend to live longer. Kind of like us. Weight gain can lead to many, many health problems.
Solomon's mother by the way, was 22 when she had him, and did lay another clutch of eggs the following year, her 23rd year. She passed away the following year, making her 24 years old. She was born in 1979. The breeder stuck to a diet that kept her lean, but growing steadily and not power feeding. The results may speak for themselves in this case.
Take care!
Billy

-----
Genesis 1:1