Should I Crossfire a Radeon 4870 & Radeon 4670?

I already own a 4870 but I need another port so I can plug in my 3rd monitor. I am well aware of Micro-Lag do you think these two would crossfire well together? There specs seem really close, and the 4670 isn't too expensive.
 
I would paste the links to the cards on Newegg but I can't copy and paste into these windows for now, WTF?
 
EDIT: It looks like its only Software Crossfire, I don't physically connect the boards with a cable. Does this matter?
 
EDIT 2: Well looks like I may end up getting a 4850 its more expensive but it has the physical crossfire cable.