Originally Posted by Nixuz
As far as the bottleneck, I'm not sure why you would care.
It's a dual core, so it's going to be a bottleneck on any games that benefit from more than 2 cores. It's a FAST dual core though, so on most other games it's going to be fine.
Certain games are more CPU, or GPU, dependent, so it's not like you'll be maxing out the 5770CF or the 6970 all the time anyway regardless.
A lot of people will say to go for the single 6970 and CF it later. Problem is, they said the same thing with the 5770 when that was new. Whenever the 7000 series comes out, they will tell current 6900 series owners to sell their single card and get a 7000 that they can crossfire later.
It really depends on how much you can get for your 5770 now, and how much you want to put into a new GPU. Another 5770 can be had for $100 pretty easily right now.
A 6970 isn't a giant leap over a 5870, and the 5770CF comes really close to a 5870.
This is a great way of putting it.
@OP, you are in abit of a dilemma.
You have two options.
1) If you go for an extra 5770 and new board, you will be stuck for options 1-2 years down the line, but you will have the latest board.
2)if you go for a 6970, you will have better performance but you will need to upgrade the board soon.
My advice: If you can get a new board/cpu and 5770 cheaper than a 6970 then go for it. It will perform slower in older games optimised for dual core (especially games that dont surpport crossfire), but for newer games i would bet that a 6 core with crossfire 5770s would beat a dual core and 6970.