Even though they are the same res the monitors you are proposing are different sizes so things won't lineup properly from the middle screen to the side screens. When I first got my 5870 I decided to try out Eyefinity with my existing 22" Samsung (1680X1050) and added a couple of Samsung 20" 1680X1050) on the sides. The difference in sizes meant nothing lined up and it drove me nuts. I ended up buying 3 identical AOC 23" 1920X1080 monitors. The other advantage of having identical monitors would be that the color settings should match right out of the box. Trying to get the 3 different montors to give the same colors was impossible.
My bezels are wider than I would like but the price of the monitors was too hard to resist.