A brief technical guideline available from Superior Essex discusses the practicalities of using installed Category 6 cabling to support 10GBase-T. The document explains the historical development of Category 6A performance levels to ensure 100-meter support of 10GBase-T. It then says, "While Cat 6A is the twisted-pair solution of choice for 10GbE performance up to 100 meters, this does not mean that the installed base of Category 6 cable will not support 10GbE, particularly at shorter lengths."
The document then references TSB-155-A Guidelines for the Assessment and Mitigation of Installed Category 6 Cabling to Support 10GBASE-T, and includes the following statement: "Note that the title references 'installed Category 6.' It is highly recommended that new installations intended to support 10GbE meet Cat 6A, regardless of length."
Nonetheless, the document from Superior Essex overviews some of the elements of TSB-155-A and includes recommended steps for mitigating alien crosstalk in Cat 6 systems.