I experienced pretty much the same as soon as patch 3.06 hit (though my laptop is a crappy i3 model, so framerate was beyond unplayable pretty much at all times and in all maps).
It ultimately turned out to simply be an issue of outdated NVidia drivers, and as soon as I downloaded the most recent ones the problem fixed itself and framerates returned to normal (well, almost normal, but that's mostly a combination of Howling Abyss being more graphically intensive than SR and my trusty lappy getting older by the day :/ )
If you already have the latest drivers installed, then I'm afraid I can't help much :(