Well, for that particular application, that might be your better choice. I didn't realize at first that the model you selected was the Eyefinity 6 edition. Do you have all the appropriate adapters you will need? Also, do you plan on gaming across all six? In that case, you might need a second 5870 anyways.
Fortunately, I do have all of the cables I need already and I most likely wont actually be doing a lot of gaming on it, so I think the single will be fine. I basically just need a lot of open charts/windows up with the job I have and thus the 6 monitor thing will drastically reduce the time for looking between different charts by not having to minimize/maximize a new tab every 20 seconds.
That would be frustrating on 1 or even 3 monitors. I believe, someone correct me if I am wrong, that if you are not gaming a lot, 2 5770's would be adequate in a non-crossfire configuration. That would give you 4 DVI ports (or 2 DVI/2 HDMI as I believe the HDMI shares bandwidth with one of the DVI ports) and 2 Display ports. That would save you from buying 4 adapters and still allow decent gaming on a single monitor at 1080p. Also, that would save you about $100.