Isn't the entire point of eye finity not at all the resolution but the positioning of the screens?
IE its supposed to emulate peripheral vision, which increases the realistic feel in games. Having the same res squashed down into a single 30" screen is completely pointless, because its not about the res, its about filling out your vision with the game, not concentrating that game into a smaller space.
Eyefinity, the vision filling reason, could be done with 640x480 res massive screens, I'll point it out again, the reason is NOT the resolution.
Another fairly key point is the ability to "curve" the displays by angling the left/right screens slightly. There was acutally a stunning "wrap around" type screen on display that did look truly awesome, and most likely extremely expensive, but it was bezel less I believe and probably Oled based.