The problem is youre not going to find anyone with any hard evidence for or against them. Most people just jump on the "they're stupid" bandwagon without any knowledge.
Its not a matter of how much boost, necessarily, its a matter of how much power the stock sleeves will take.
If you have good tuning Ive seen/heard/read of people making 400-500hp on stock sleeves - its all in the tuning.
Im for them on mild power (I wouldnt go above 350, but thats because mine's a daily driver) and will be purchasing a GE guard for my ls-t