i see no harm in cutting it and seeing if there is a difference, but to be honest, I don't think your going to see an improvement, I can't imagine its going to restrict enough of anything to make a dam bit of difference.
however...
if it doesn't pan out... you can replace the stock nozzles pretty cheap, (I was trying to sell an extra set on fleabay for a couple of months, quit trying after reducing the price to $6, just gave them away for the cost of shipping.)
I agree that I prefer the aftermarket reduction nozzles but when mine were put on we did other changes as well so I can't say from experience how much difference it really makes either.