the previous owner of the car was using mobil 1 10w-30 synthetic till 92k and platinum dual tip plugs. I switched to bosch super dual tip copper plugs the second I got it and I find the idile is not as steady as I'd like and in the 10w-30 just doesn't seem right for the car.

So this weekend I would like to switch to 10w-40 amzoil, and NGK irridium plugs. It's not that I have a thing for 10w-40 vs 5w-40 or amzoil but they have it at my favorite local auto parts place and I've heard amzoil is quite good.

I'll be at 93k soon here, advice?

I generally use thicker in the summer(Mobil 1 15w-50 or 10W-40) , then switch to the thinner weight Mobil 1's in the winter. No experience with Amsoil.
At 75k, our 30v has no leaks and gets great MPG. I have found NGK copper plugs have better detonation then the plats in our car. I also change them out frequently(every 15-20k). If the idle is not as steady, clean out your throttle body, replace the fuel filter, and install a can of Chevron Techron concentrate. I think you'll , find a vast improvement after that.
Oh yes, if you find oil in the intake, you might have a clogged pcv, that can also effect the idle.

BKR6EIX for NA V6.