Need help choosing video card (a quasi noob)

This time I chose not to build my own computer (the current build is nearing its 5th birthday) -- just not enough time during retirement to get all of the things done that are on my llist, so I am biting the bullet and buying a computer and need help with two aspects of the video card -- one an opinion and one a specification that I cannot find.

This will be my first experience with nVidia chipsets. The mobo is an nVidia 790i Ultra SLI running an Intel Quad 9450.

Question 1) Realizing that most of my computer work will be with Photoshop in the digital darkroom and a few games, which of the three following choices are the best bang for my bucks (only three choices available, so the ATI brand that I have used for over a dozen years is out)
--GeForce 9800 GT 512MB SLI
--GeForce 9800GX2 1024MB (single card)
--Geforce GTX 280 1024 MB (single card)

Question 2) My NEC SpectraView monitor requires a two-way communication with the video card called Display Data Channel - Command Interface (DDC/CI) and will not correctly function without this capability. I could not locate anything on the nVidia Site regarding this spec nor any place to send an email to customer support for an answer. Thus, I must ask it here -- do any of the above video cards have the DDC/CI specification?

Thanks,

MrSpurg