x2 heatsield and i use fiberglass weaved sleeves for the wires (summit or jegs has em)
i use the graneteli (??spelling??) solid core wires and i have not had a problem with interference (fingers crossed) and that is with a potent ignition
Design Engineering DEI 010504 - DEI Protect-A-Boots
i think the biggest killer of wires is when they are handled (constant bending) i am very careful not to overbend my wires and always use elec. grease in the boots