Looking all over may different sites some give the impression a 3tb drive will show full 3tb without a UEFI bios and without the expansion card. What most sites give the impression of is you only need the UEFI bios is if you plan to use it as drive to install windows on and boot from it. I know you certain versions of windows to support it which i do run windows 7 x64. I would like a straight answer if I will get full 3tb without the extra card on a p55 board. I haven't been able to get a straight answer on the matter.

need bios update from EVGA , gigabyte and asus make this update to use 3T on P55 mainboard

almost 3 weeks and since no other post cept for a bios update which there is none, reading on 2 sites both are saying as long as you have a 64bit OS that support GPT you are fine to use full 3tb for a secondary storage drive. Only time you will run in to an issue is if you try to boot from it then you will need the UEFI.
 
http://www.anandtech.com/...-3tb-drives-reviewed/2
 
http://techreport.com/articles.x/19871

I make a test on  SATA3 card , win7 64 boot ok just need a card with bios boot option , rocket620 is fine a have this for 50€