Helo Amigo, im I'm pretty sure u you can do the bosses right now.
Ofcours, u Of course, you have to understand something easy - More lvl ,easier, and faster. I would recomend recommend 350+/400 for make it confortable comfortable and not sufering.
suffering.
Anyway for add more information, bosses like Hellgorak will never been defeated Solo, for kill this boss u you need to use 5 convince creature rune (atleast) (at least) for make damage on boss, and u you need minimum 3 ppl people for kill this boss.
I hope i I helped u
you
Greetings, Gleemody