Ok, this is a 3 part question, so here goes! 
I'm currently looking at purchasing an R9 280X to Crossfire with my HD7970 Vapor-X.
As 7970's, for some reason, cost MUCH more, I was looking at getting a 280X instead as I believe they Crossfire just fine with 7970's (7970 Vapor-X ~£338 and 280X Vapor-X ~£270. Absolutely no idea why the former haven't dropped in price yet as they're essentially the same card!).
My first question: As the cheapest and most expensive 280X's differ in price by almost £80, is there really that much difference? I know the best option (and most likely the one I will go for) will be to get another Vapor-X but is there really that much difference between the models? I currently have my 7970 clocked at 1175/1650 stable with temps under 70C at max load, would any of the cheaper cards overclock that high? Also, would compatibility be an issue running cards from different manufacturers?
Second question:
This is my current set up.
Motherboard - GA-990FXA-UD5
CPU - AMD FX-8350 (overlocked to 4.8GHz)
RAM - 16GB Kingston (4x4gb)
GPU - AMD Radeon Sapphire 7970 Vapor-X
PSU - Corsair GS800
HDD - 120GB Samsung 840 EVO SSD (+ 2 other cheap HDDs for storage)
Displays - Dual Monitors + Oculus Rift Dev Kit
Displays are currently running at 1080p (apart from Oculus Rift which runs at 1280×800) but I am debating purchasing a higher resolution monitor or buying a third and running games across 3 1080p monitors but this wont be for a while. Part of the reason for this purchase is to get ready for the Oculus Rift consumer release, which will have a higher res display (1080p or higher) as I believe a single 7970 might struggle to display 3D with head-tracking at those resolutions.
From what I can tell, my PSU should be able to run 2 7970's in Crossfire just fine but I'd like to be extra sure before I purchase another as setups and watt usage can apparently vary quite wildly. I've also checked and my CPU seems fine for a Crossfire but, again, you can never be too careful
Third question:
Would a Crossfire actually be recommended? As I already have a 7970 and, from what I can tell, AMD have made huge improvements with Crossfire, this would obviously be the cheaper option. But I guess a single GPU setup, say a 290x, would be more "stable"? This would obviously be much more expensive but would it outperform Crossfired 280X's? From what I've read, it seems the 280's would be a better choice.
Sorry for so many questions but when this much money is involved I'd like to be EXTRA sure!
Thanks!
I'm currently looking at purchasing an R9 280X to Crossfire with my HD7970 Vapor-X.
As 7970's, for some reason, cost MUCH more, I was looking at getting a 280X instead as I believe they Crossfire just fine with 7970's (7970 Vapor-X ~£338 and 280X Vapor-X ~£270. Absolutely no idea why the former haven't dropped in price yet as they're essentially the same card!).
My first question: As the cheapest and most expensive 280X's differ in price by almost £80, is there really that much difference? I know the best option (and most likely the one I will go for) will be to get another Vapor-X but is there really that much difference between the models? I currently have my 7970 clocked at 1175/1650 stable with temps under 70C at max load, would any of the cheaper cards overclock that high? Also, would compatibility be an issue running cards from different manufacturers?
Second question:
This is my current set up.
Motherboard - GA-990FXA-UD5
CPU - AMD FX-8350 (overlocked to 4.8GHz)
RAM - 16GB Kingston (4x4gb)
GPU - AMD Radeon Sapphire 7970 Vapor-X
PSU - Corsair GS800
HDD - 120GB Samsung 840 EVO SSD (+ 2 other cheap HDDs for storage)
Displays - Dual Monitors + Oculus Rift Dev Kit
Displays are currently running at 1080p (apart from Oculus Rift which runs at 1280×800) but I am debating purchasing a higher resolution monitor or buying a third and running games across 3 1080p monitors but this wont be for a while. Part of the reason for this purchase is to get ready for the Oculus Rift consumer release, which will have a higher res display (1080p or higher) as I believe a single 7970 might struggle to display 3D with head-tracking at those resolutions.
From what I can tell, my PSU should be able to run 2 7970's in Crossfire just fine but I'd like to be extra sure before I purchase another as setups and watt usage can apparently vary quite wildly. I've also checked and my CPU seems fine for a Crossfire but, again, you can never be too careful
Third question:
Would a Crossfire actually be recommended? As I already have a 7970 and, from what I can tell, AMD have made huge improvements with Crossfire, this would obviously be the cheaper option. But I guess a single GPU setup, say a 290x, would be more "stable"? This would obviously be much more expensive but would it outperform Crossfired 280X's? From what I've read, it seems the 280's would be a better choice.
Sorry for so many questions but when this much money is involved I'd like to be EXTRA sure!
Thanks!
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