Display port is a newer connection than hdmi which will support 4096 x 2160 resoultion. Hdmi will support this too but only hdmi 1.4 so you will need to check the vid card specs. This is only important if you are going to buy a UHD TV with 4096 x 2160 resolution (This is where the 3Gb VRAM will help too).
To clarify about the dp adapters, passive just converts the signal to DVI or HDMI (I have not seen any active dp > hdmi adapters myself) without changing timings/frequency of the output, an active adapter is actually powered by the display port (Or have a usb connection for power) and adjusts the timings of the output (Not controlled by video card). Active adapter can look exactly the same as passive so u would need to check what u are getting. Some have active printed on the adapter. Eyefinity is better if you want to do more than just 3x1 landscape, ie: portrait mode, dissimilar monitors, 2x2, 1x3, 5x1, 6x2.
Sapphire FLEX edition (Look for VAPOR-X, there is a 6Gb version) cards can do 3x1 eyefinity without using a dp connection.
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If the monitors u buy are EXACTLY the same (As was stated sync polarity is important) then nvidia surround will be no problem, BUT make sure to use the supplied VGA/HDMI cables. I had a situation with a nvidia sli setup (2xGTX560's) and i purchased a VGA cable for extra length and it changed the way my monitor was detected by windows (went from generic PnP to non-PnP) and this would not allow surround to be setup (Was sayin WTF for an hour before i figured it out).
Nvidia GTX 780 is the best card out atm, so if you need more power down the track sli is a viable option. (Might need to upgrade power supply or get 800w+ now....)