moknowsbest
What is the best way to find out my cards capability...tweak it little by little as jays2cents suggests?
Yes. One card at a time to learn each cards limits and then you know the best to hope for in SLI (the weakest link). Make the strongest card the primary for times when you have to disable SLI.
No one here is a god, but there is a wealth of information collectively. Before too long, you'll be in the fray helping the next new person.
EDIT: Some may Sajin is, come to think of it.