Recently heard about Litecoin, but i have a fair idea on Bitcoins.
If you are into mining, then it isn't a good idea in spending on an advanced GPU for the purpose.It doesn't take advantage of a compute architecture but has a more parallel nature(integer perspective).
Even the older VLIW based radeons have a more hash rate than the current GCN cards. Mining benefits from a peer to peer network.
So a single system isn't an ideal one. Multiple systems are necessary and the correct term would be "distributed computing". You need multiple systems connected to a network in order to achieve maximum hashing frequency. So the decision of going for a single 7950 or upcoming 8950 isn't an ideal choice from a mining only perspective.
There are other FPGA miners available which has a better hash rate at a lower pricepoint. When used in packs (preferably 4 ), one can achieve close to 4 GH/s, and one is definitely going to need this kind of performance for efficient mining. GPGPU for mining has a quite a bit to prove before becoming a standard.
As you should already know, mining algorithm is basically involves reversing a secure hash, notably the SHA 256 in order to create a new block (The central part of the whole mining process. Won't go into details as you should be already knowing it). Now SHA 256 hashing performs poor in nvidia cards because of their inability of efficient integer computation, and SHA 256 is mostly (completely) integer based. VLIW shines here because of its multiple ALU design per SIMD. It can do the integer functions better.
Its even better than current GCN in SHA hashing.
This is completely regarding bitcoins. You can throw some light on Litecoin, but i assume they are mostly same.
One thing i would also like to point out that you don't need a specific GPU having better compute resources to learn open-cl. Open-cl runs on CPU too and you can run code without any complexities arising.
