The overheating isn't causing your laptop to lag in games due to the heat itself. I have the 4 core version of your laptop, which is essentially the same, and the system is designed to "throttle", i.e. downclock the speed of the graphics card when it hits a certain temperature, in my case it is 84 degrees C. I think Dell added this as a "safety" feature, although in my opinion it's completely unnecessary and hinders gaming performance since most GPU's can handle up to 105 C before they suffer adverse effects. When the GPU throttles you will certainly notice a lag in gaming. The 4 core version got a BIOS update that removed this feature, which removed all lagging during games for me. Now I just have to use a temp. monitoring program to keep a close eye on the GPU temps. I'd check the Dell website to see if there is any new BIOS updates for your laptop. Also, to avoid ever hitting that throttle temperature, a good choice in my case was to get a laptop stand with a built-in fan. I use one when I game for long periods and it reduces my average temp's by about 10 C, which helped me to never hit that throttle temperature (even before the BIOS update).