hmm unfortunately your performance seems about in line on the high settings and the witcher 2's lower settings seem to not provide much more performance for most people. What you need to remember is laptop graphics card's arent comparable to their desktop counterpart. youll find that the 5870m is about the same as a 5770, which isn't a spectacular card and your 5850 would be even less than that.
Best you can hope for is further optimisation to the lower settings because atm they really dont improve fps as much as their lack of detail would lead you to believe.
2500k 4.4ghz, 8GB DDR3, PowerColour 5850 1gb, 520HX, 40' Sony Bravia W