Power valve

I have noticed for awhile now that my car runs excessively rich when I first crank it up. In my mind it was "big cam" and "big carb" is going to cause this until it warms up. In reality however it is still a bit on the rich side for instance idling in the garage after being drove enough for it to warm up. The 4 idle mixture screws on my Holley HP 750cfm DP are only backed out ¾ of a turn each. My spark plugs are black and sooty and never burn as clean as I would like them. So what I have is....

Ancient Mopar cam .474/.474 280/280
10:7 compression 30 over 360
Performer intake
1" open spacer
TTi headers
Stock mopar distributor with Accel 300+ ignition (rev limiter)


The motor runs fine, has great torque, and will burn the tires.... but she is a little rich. I don't ever see black smoke when I get on it or it idling however. Just that eye burning fumes.

Now the other day I was browsing around and came across a thread (that I'm subscribed to) and read something interesting. A fellow member was running the same cam. I moved the total timing to 36 so now vacuum at idle is 8hg and climbs ever so slightly to 9 This is a manual transmission car.
Go here and scroll to post 46 and you will understand a bit more clearly.

http://www.forabodiesonly.com/mopar/showthread.php?t=81499&highlight=power+valve&page=2

Now after reading that one post I have ordered 3.5 hg power valves and going to try that. I will tinker with the springs later in the distributor. Also going to try a 1" 4 hole spacer. I have always wanted to try the 4 hole.

So I believe I am heading in the right direction with the power valves since the stock power valves are 6.5

Other than torque what else would I gain by going with the 4 hole instead of the open? I'm thinking it will narrow down the circuity of the carb if you will.
thanks,