A Lvl 8 can be killed by a lvl 5, I did it but it wasn't easy. First you have to have decent gear. Use your bow/spell attacks and stay clear of it if it's a melee enemy. If its a ranged or magic enemy, close the gap quick and avoid its attacks with jump and roll tactics. Then close to melee and pummel it til it either dies or tries to run. Either way, keep on it and watch that you don't get ambushed by it's buddies. It's frustrating at times, but the XP yield for killing over your Lvl are great.
