Lightning pauses you also.
I prefer single spell for Heavy's and Comps.
Double spell for the regular bow (veloc/lightning)and crossbow (veloc/fireball).
To be honest I don't use my crossbow as much because it doesn't belong in a group pvp field anyway. You want to dismount (heavy), equip last to a para (regular bow) to stick the guy you dismounted, mortal (regular bow). That's how you properly gift wrap that guy for your guildie Twinkle McNugget to finish him.
I'll have that 4/6 setup also, and x-fer to the home shard in a week, now that they finally put this patch through.