Upgrading graphics cards in laptops is a bad idea imo. If you're looking for a gaming laptop get the best graphics card you can and stick with it.
If you want upgradablilty you're far far better off putting a nice desktop machine together.
Also remember that graphics card models in laptops aren't comparable to desktop parts- the 'new' 880m for example is a slightly down clocked GTX 680, there are much faster cards available for desktops.