Earlier in the product life cycle IBM commissioned a competitive switch test #211108 by the Tolly Group in March 2011 that does report on buffering. Summarizing:

Refer to the disclaimer at the top of page that says rumor, innuendo and extrapolation. Tolly attributes something more than 100 percent of the buffer is available for microbursts. That seems suspicious. The buffer imputed to the Cisco 5548 switch also exceeds the manufacturer's claims. Unlike other tests reported in this Tolly paper, there is no RFC that says how to measure microburst capability. Absent some real skullduggery, the relative results are probably useful.

The Lippis Report mentions RFC2889 when they describe their microburst measurements. But if you read what they are saying carefully, they cite only the test configuration. There was no microburst test defined in August 2000. The RFC is useful for its framework of how you should think about this sort of test, but microburst tests have not been standardized.

Regardless of whether IBM might have a dynamic buffer control that I missed when I read the manual, the warning stands: Use of particular silicon is no guarantee of availability of a feature absent its presence in the switch data sheet or other documentation. Reliance on reports from a for-hire tester of something not claimed in the data sheet is also probably not wise.