For these new machines, OS X provides the option of using the discrete GPU and the integrated GPU, or just the integrated GPU for longer battery life. This control is found in System Preferences -> Energy Saver-> Graphics.
You can try setting this to "Higher Performance" in OS X and verify after the required logout/login. Restart back into OS X to confirm the setting, then restart in Boot Camp to see if your Windows 7 performance is any better. There may be a similar setting in the Boot Camp drivers for Windows 7: I don't use Boot Camp personally, but I've read some of the features of the newest Macs might not be available to Windows until Boot Camp is updated...