I am not religious about specs, but I also don't have any reason not to follow them with my AGM. I assume they didn't just pick those numbers out of a hat.
If there is nothing to be gained by going past what they advise, why do it? It is the old risk/reward game as usual.
That is not saying Mex's advice is not good. If I had a good reason, my notion of the risk is much reduced by what Mex has posted here.
You have to take everything you hear and read and see how much money you have and then make your own call.
My fast charging on generator is all with Wets, not with AGMs, and I am not shy about getting the gen time down by using high amps. I can always add water to my Wets if I over-do it, so the risk is low and the reward is high.
I do think the risk with AGMs is higher, perhaps a lot higher, so I am glad I have Wets for that job. One less thing to worry about :)