Crescent Moon is another good choice (I didn't see it mentioned, but I kinda skimmed the thread). ITD is a great help against anything but bosses, and those can be smacked around with Smite if you're having a hard time hitting them. The ctc Static Field will help a bunch against mobs, and you can slap it in a phase blade for speed. Check your breakpoints before choosing the base item, though; phase blades are fast, but the damage is less than stellar. If you don't need the speed, go with something hurtier.
CM also opens up the possibility to use a low-level Holy Shock aura or Vengeance as a backup for PI monsters; the penalty to enemy lightning resist will help an otherwise underpowered backup be more effective.
I'd recommend against Kingslayer in a phase blade because of the low damage. Crescent Moon offers a little less raw damage, a bit less IAS, no crushing blow, and no prevent monster heal, but it's also a lot cheaper, gives ITD, and Static Field is kinda like crushing blow over a group. Kingslayer's big selling point is the oskill Vengeance, and that works best in a higher-damage weapon, as non-paladins won't have the Conviction aura or synergies to boost its effectiveness.
The Treachery runeword armor can give you big resists (once the Fade kicks in) and IAS, which frees up other gear. It also means you'll be constantly running with active Venom, offering a bit more damage. It's short duration, and truncates item-based poison damage sources to 10 frames (0.4 seconds), so don't rely on it as a solution to prevent monsters from healing. Open wounds or prevent monster heal mods will do that, and they work against poison immunes. Treachery armor is also great on all but the Act III mercs.
I know you said no other software besides GoMule, but if you're willing to install the runeword mod (gives us SP people parity with b.net, as far as runewords go), then Harmony and Insight are excellent and cheap options for Act I and Act II mercs, respectively.
If you can find it, Headstriker is an excellent weapon. It doesn't have IAS, but it's got big damage, scaling max damage, and scaling deadly strike (at clvl 67, every strike will be a deadly strike). Sureshrill Frost doesn't offer great physical damage, but it gives decent cold damage, cannot be frozen, and it freezes things (great for shamans and the like).