From what I've read, you'll probably only gain 10%. Think about it, how much more powerful is an 8200 over a 8600gts? (The 8600gts is probably 5x or more powerful than an 8200).
from what I understood it shares the workload of the 2 gpu's right?? so then if i gain 10% its really a good news for me ... but then will my gpu benefit from this like in terms of life expectancy and in terms of stress??