i've use i5-2500k @4.4Ghz about 1-2 years ago, and i can confirm its run 80fps+ paired with gtx 970 on fhd
so yes i5-2500 is worth the upgrade, and i suggest you pick i5-2500k and overclock it, dota likes high clock speed, i think with stock i5-2500 you might get a little frame drops in clash