It depends on where the 5970 is clocked at.
if the 5970 is at 5870 speeds there is hardly any diffrence.
keep the 5970 and get a 5850 for tri-Fire! :P
Well I can tell you, at least for my paticular 5970, I couldn't get close to what I am achieving on my ASUS ROG 5870s...(1000 core, haven't touched memory , yet).
Also, if Eyefinity is a concern- which it is for me- tri fire isn't really an option. That's why I went for the fastest dual card solution I could find: 2 of the Matrix 5870s.
