Dell R510 12 Bay SAS Backplane - SAS/Sata limited by backplane or controller?

Hi,

Question as per title really.  I'm interested to know if the SAS backplane in the 12 bay R510s is limited to 6G SAS / 3G SATA due to the expander or the default controllers that ship with it?  I'm looking at one for a storage server but would utilise a LSI 9211-8i in IT mode that supports 6G SAS/SATA it would be good to get 6G SATA speeds if possible.

Is that possible, or am I limited by the backplane expander itself?

Thanks,

Chris