I had all sorts of problems with my GTX 880m -- two generations back from your card. Terrible performance on the lowest setting and crashing, crashing, crashing. Which was strange because my 3.3GHz laptop usually handles everything. And then I found some advice buried deep in a forum somewhere.
Try *under* clocking. I used MSI afterburner to set my clock to -42 and the game has performed flawlessly. I think Larian has a problem with GTX cards -- for some reason my card was spiking to maximum output / max heat all the time. All of which is ironic since the NVIDIA flashscreen pops up every time I start the game.
