This. My Sony Vaio S13A under full load in BF3 has never exceeded 78C even on the hottest day here in California. This is with the stock TIM. And it's even overclocked to 900/1000 from 500/1000, so I have 650m clocks on my 640m LE. CPU is an i5-3210m.
Also keep in mind that the laptop is very thin. It's only 0.85" at its thickest, in a 13" form factor.