Matthew. Let me give you some sound advice here mate.
Crossfire and SLI are not trouble free painless entities. They are a PITA at the best of times. Let me list a few examples of the troubles I had with 5770CF.
Now on paper 5770 CF was just breathtaking. Imagine the horsepower of something that could easily brush aside the 5870 yet cost £100 less? (pair of 5770s were £250, at time of buying the 5870 was £350). It was mouth watering. Infact, so apparently good were the 5770CF that they absolutely crapped on a 5870. So, smart money was on 5770CF yes? No. In hindsight I wish I'd have got a 5850. And, here are the reasons why.
1. Drivers. AMD/TI whatever they call themselves now are notoriously known for bad drivers. Any company that has to release drivers almost daily has got issues mmkay? Certain drivers were so bad they would bork my Windows install forcing me to back load an image via Acronis.
2. No game at launch will run perfectly with Crossfire. If you're a gamer and not a benchmark freak then this is annoying at the best of times and downright infuriating at the worst. Certain games will run well on one card even with buggy Crossfire, meaning you won't even realise. Now that's cool in the case of the 5970 and 5870CF for example but on urine week single cards like the 6870 this WILL stop you running games with all the trimmings. I had issues with pretty much every game I ever ran on launch. Just Cause 2 required me to wind the settings right down but even that wasn't enough. I had to run my monitor 'out of resolution' at 1440x900 or something daft and it caused horrible ghosting just to get the game to run right.
3. Even with the certified Crossfire profiles downloaded and installed onto your machine that doesn't mean they will actually work. Take NFS : Shift for example. In the end I had to rename the .exe to grid.exe just to get it to use Crossfire. Even though ATI assured their users that it would definitely work 100%. And, all this hassle of constantly checking that it is working and running FRAPS to make sure (by monitoring the FPS count) is kind of like sand in your bum from being on the beach. At first you don't mind because you have had a lovely day out, but when the chafing begins it is irritating.
4. Even with Crossfire profiles, patches, new drivers and all sorts of buggering around certain titles just refuse to work in Crossfire this is strongly applicable to Borderlands. It simply does not work in Crossfire, will not work in Crossfire and if you make any attempt to run it in Crossfire it will simply crash to desktop. Gearbox were contacted about it and their advice was to disable Crossfire in the ATI CCC. In other words they simply didn't care.
5. Crossfire and SLI are still not widely acceptable methods of gaining cheap horsepower. They are aggro, hassle, and fall back to drivers which you then have to rely upon. Now whilst AMD put a lot of time and effort into this they do tend to concentrate on other things first, like making money. And whilst sometimes Crossfire may work out of the box (due to luck more than anything) that isn't guaranteed. After all of this you realise that in SLI and Crossfire you absolutely must enable Vsync in order to avoid stutering and tearing and it becomes all the more pointless over buying a comparitively priced single card.
By disabling Vsync you can please yourself with high FPS counts. However, if you are a true gamer who actually wants to sit down and play a game hassle free? then I wouldn't touch Crossfire with a barge pole.
I almost bought myself a Micro ATX board with one PCIE slot just to stop me from being tempted into wasting time and energy on mutiple GPUS. The noise is horrific (yes, even with 5770s) the top card idles at a higher temp however you can't set up profiles in Afterburner seperately so to keep the temps in control you have to have them both doing the same fan speeds and the noise levels are, quite frankly irritating. Power consumption doubles to the point where I could have been running a 480 and my rig would have been cooler and quieter whilst using less power and so on.
In certain circumstances multiple GPUs are a godsend. In folding they are amazing, however, you don't need to SLI them for that. In benchmarking they are fun (if that floats your boat) but in complete honesty in actual gaming they are less than hassle free. They will get on your nerves sooner or later.
As an ex Crossfire/Quadfire/SLI user I would never go back. It was fun, been there, seen it, done it, got the photos and the Tshirt. Now? I'll take the easy life thanks.
