install program such as speedfan and in options set it to show cpu temperature in system tray when program is minimized so you can watch it while playing.
it shouldn't go over 70 degrees celsius while playing.
when intel processor starts to overheat, it throttles down itself as passive method of cooling down resulting in slower performance.
trust me, i know everything about this, i have 14 years old pentium 4 desktop computer, still works flawlessly because i open it once a year, suck all dust with vacuum cleaner, and i put some new thermal paste on cpu.
i do same with my asus laptop.