Remember what Grievous did on the Tartakovsky's Clone War Series: he was a ****** , not a coward.He was fast,4 arms + using legs + spider-like abilites+ using walls and cellings. Tough fight,but he'd win a duel.
All out war?Tough call too.Maybe a ruined galaxy for an Android to rule?
And -that- series has been made non-canon. It also made the cast obscenely more powerful than they were ever depicted in the Movies, EU counterparts and later the newer TCW series. You watch EP3 and TCW, he's a pure-bred coward. Having four arms doesn't mean much. There've been Jedi and Sith like that before.