I would assume the irons are accurate or else I would hope remington wouldnt them on their products but I can not say for sure...

The reason you dont see them tapped out on most of the 870 models is because the top of the chamber where they are normally tapped is too thin. (not saying it cant be done)

I have the 870 Super mag for turkey and ended up going out and buying the model 870 Express Synthetic Deer. The other thing I like about the new one is the stock is a rifle style (raised stock), which makes shooting with a scope more comfortable.

I dont think you can go wrong with your choice. There are always advantages and disadvantages. You may also want to look into the Winchester model 1300 combo, which comes with both barrells and is already tapped. My father has this model and changed out the irons with a fiber optic replacement set, which maybe something you might want to look into if you decide not to go with a scope.