I find HLD to be a necessity on ranged items. Otherwise, even at 120 weapon skill, I miss a ton. Spell channeling will effectively take two mods, but at 120/120 focus/mystic the "enchant" spell will grant your weapon 60% hitspell and spell channeling with fc -1 for ~2.5 mins. That might not be long enough to be useful in a long pvm encounter, bit you could compensate with 3/6 jewels or by adding fc1 to weapon. Slayers are great but tale up a lot of room. If you have tactics in your build velocity is a good choice for weapons with moving shot (repeater/comp bow) but I feel more comfortable with hit lightning in most cases as velocity requires you stand in a sweet spot towards the end of your range to do maximum damage. Hit mana leech is nice but fairly useless on ranged weapons because of the necessity of swingspeed (I think 37 is the most you can have at 40ssi). Also, SDI increases hit fireball/hit lightning damage.