As relating to boot drives, you are right. However, as relating to data drives, many motherboards on the market today can make use of the full 3 TB capacity without UEFI. Each particular piece of hardware requires hands-on testing to make sure one way or the other.
As pertains to this particular hardware, I currently have some 3 TB Hitachi CoolSpin drives that I am going to be using to test out all the motherboards and controllers I have over the next couple of weeks. The Biostar A880G+ is one of the motherboards I will be testing. If you aren't in too much of a hurry, I suggest that you might want to wait for my test results before making any purchasing decisions. I will try to be expedient in my testing. Feel free to PM or email me for progress updates.
I think i'm just going to start with 2tb drives and will add 3tbs along the way. Only other question is: Can I use a Sempron 145 in place of the 140? Only reason I ask is because it is $15 cheaper on Amazon. Thanks.