Speed sub-stats are almost always your best option. But generally you are better off using your speediest mods on either damage dealers or support characters that give turn-meter (like Stormtrooper Han or Jawa Engineer). I would slap a bunch of potency mods on Old Ben, even Mk I and MK II will give great set bonuses. He already has enough health, and he doesn't need offense or crit damage. Some tenacity sub-stats wouldn't hurt either.
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Could be on a newer servers where there aren't a ton of EPs.
Get off your dam high horse... arena is not the only place where characters are used.