Might is good for increasing your physical damage and your mercenaries damage. You could also use a Defiance mercenary for the added defense if physical damage isn't a priority.
I would use a ethereal thresher or giant thresher for the Infinity base since both have a weapon speed of -10. I would use an ethereal Treachery for the armor. 45% IAS, Fade and CTC Venom are nice mods. If you are trying to hit the 75 IAS BP, you need 30 additional IAS on the helm. Andariel's Visage with a 15 IAS jewel is the cheapest way to hit 9 FPA. A 30/15 Fire Resist/IAS jewel would be the more expensive jewel to use to cancel out the -30 Fire Resist. If you don't care about the 75 IAS BP, Fortitude is a nice armor for additional damage and Gladiator's Bane is nice for survivability. For helms, a Guillaume's Face is a nice way to increase your mercenaries damage. You can also use a Vampire Gaze for increased survivability. Delirium can be used for crowd control. It's really up to you at the end.