distributor cap and wire question

well, ive had this misfire/backfire problem for a long time now
thinking it was carb, cam or other related i just kind of didnt rev over 5500
the misfire is almost guaranteed at 6krpm

i have the performer cam, stock heads, 2.8 gear, c4 tran, 2 different intakes and carbs, headers, 2 inch pipe (i think), h-pipe, dyno max super turbo muffs
some new(4 years old or so) stock distributor (i assume, my dad purchased it)
with the small cap, taylor wires, pertronix ignitor and msd 6a box
(had problem before ignitor and msd box)
electric fan on a 289ci

i was rereading the smokey yunich book and it said alot of problems from engines are from ignition misfire caused by crossfire in the distributor cap, grounding the ignition wires or crossing the ignition wires
well, i have some cheapo wire separator - so my wires still cross at some places and touches the block on some places
smokey said the standard 40 year old cap is not good, and to get the big one

so 1st: i need a good wire separator
2nd: i need a large cap that will work with my stockish distributor

not that i care to rev 6k, but im worried i might be losing power at the lower rpms and maybe some gas mileage...
thanks in advance,

holiday bump

thanks for the replies

what are some other symptoms of a bad distributor - although i think i had this problem when it was brand new - ive pulled the distributor out before (cause i thought it was leaking oil, could i have screwed something up (besides timing)