I tried using the 4650, but it stuttered a bit with 1080p video (noticeable when the 6450 was doing stuff as well) and also the animations on Windows 8 weren't super smooth. I mistyped in the initial post; I had a 6450 and 4650; not a 6850. I replaced the 4650 with a 6670 which is doing nicely. So, I have the following setup:
ATI 6670 - one 27" catleap and one 42" LCD television
ATI 6450 - one 27" catleap
integrade intel HD4000 - one 22" monitor in portrait
This works well for my needs considering I do no gaming at all.