MD3860i INTERNAL SAS buss speed

We are testing a MD3860i prior to putting it into production. This question is about the INTERNAL SAS buss speed - as reported by the management console for this MD3860i. All drives are 12Gb/s - 8 x 4TB SSD's + 52 4TB NL SAS.  The internal SAS buss will only run at 6Gb/s. All internal reports come up 'Optimal'.  Reading the literature it appears to be sold as a SAS-3 system which should run at 12Gb/s. FYI - the internal LSI chipsets on the controllers are 12Gb/s capable as is the cabling to the drive trays.  We are being told by our supplier that a MD3860i will only run at 6Gb/s internally - never 12Gb/s. Could a Dell Storage Expert please give a definitive answer as to whether the internal SAS buss from the RAID controller to disk arrays can run at 12Gb/s. - yes or no. Thanks in anticipation.