we tend to make recommendations based on the needs of the OP. if he won't ever NEED that kind of power, then recommending excessive power is simply a waste and would be considered poor advice. it's like recommending someone to use 106 octane aircraft fuel in their toyota tercel it will never need that grade of fuel and it's a waste to having to drive to the airport to fuel up the commuter car
7870 is not a weak card. it still far exceeds the needs of the OP since 7870 IS in fact a gaming grade chip the card i linked happens to be one of the cards that allows for 6 way eyefinity on a single card (i'm sure there are other brands, i just picked the 1st one i saw off google so I'm not making any endorsement or anything it's just a whatever showed up on google ) which is what the OP is looking for. of the business applications i've ever seen, i have yet to see ANY "business" software that requires that much power to render.
as for practical reasons... electric usage, heat generation, acoustics... why feed a monster card when you don't need to.. of course we can talk the OP into F@H but i think that's a different agenda