What are you trying to achieve? Define what you mean by dead. Long dwell means an elastic string that cups the ball ALOT. 4-5 ms is the duration you're looking for? What are you planning to use as a main because that will also have a major effect on dwell time.
Asking for a non poly cross means nylon, which means you cannot achieve long dwell times unless you use thin gauge at low tensions. Nylon (all stretched out) would work, but it would wreak havoc on control.