If speed is your goal, widening the rear notch will get you that. You aren't removing much material at all, just enough to open up the sight picture slightly. You can also purchase modified rear sights online if you're not comfortable doing it yourself.
Making the front post smaller will make it harder to pick up on target, the wide post is easier to see. A narrower post will, however, be more precise, but nobody that I know of would ever recommend it on anything other than a target/range gun.
Per my response in the other thread,
It depends on what your ultimate goal is:
If you're hoping to increase the precision of your iron sights [for potentially more accurate shooting], Tech Sights and a KNS front ball post will be your best bets.
If you're looking to combine precision [accuracy] with a fast[er] sight picture, your standard front post and either Krebs or Mojo's rear peep sight will be the ticket.
If you're just looking for an increase in speed of acquisition but aren't necessarily looking to improve your sight picture or accuracy with the rifle, save your money and just widen the notch in your factory sight and you'll be all set.
These three options are just my opinion of course, but I have a good amount of experience with all of the aforementioned sight configurations as well as various optics setups and those were my findings after extensive use. I run Tech Sights with the KNS post on one of my SKS that I use for pig hunting and target shooting, but I've settled on the Mojo peep and the standard post for my Draco SBR that sees a lot of use at ranges of 5 yards to 200 yards in tactical carbine courses, run-n-guns, etc., while my AK-74 that doesn't see much use (other than recreational can popping in the desert) has a standard sight with the widened notch.
Granted, sights themselves will not increase the accuracy of your rifle, but can potentially increase the accuracy with which you shoot it.
Adding a dot of white or orange paint to the very top of your front sight post (not painting the post itself) will also help the speed at which you can pick it up if you're shooting in to a dark background.