An STC comparison will tell you that there is very little difference in sound performance between the two units that you are considering - both will have STC of 35.

However, if available, adding the 6mm laminated lite to option A in place of the 5mm monolithic lite will push the STC to 39.

OITC will favor the 6mm laminated over the 4mm/5mm IG (30 to 28), but the best OITC will also be using 6mm lami in the IG as well - OITC of 31 in that case.

Thank you for your help. I´ve been looking for your very useful posts all over this forum and I´ve learnt a lot about the subject.

The option you suggested is available at more than 30% extra cost. It seems a small benefit for such an extra cost, OITC 31 over OITC 30...I remember you wrote you prefer OITC over STC

Thanks again.

I just moved to my new home (built in 1958 with lathe and plaster walls and stucco exterior) and to my dismay, find the traffic much more intense than expected. I have small truck noise, and flowmaster muffler noise. No one keeps within the 25 mph speed limit, but go more like 40. Thus more traffic noise comes into the house than I thought.
I had the installer of sound proof windows come out and talk to me about their product. While is sounds like a great concept, I have such a large picture window, it would be difficult to remove the insert to clean or repair the permanent window. Which is double pane aluminum frame about 15 years old now.
I have looked at the Quiet line windows. They look impressive. I would get one with one laminated pane of glass and two regular panes. The rep recommended a rating of 41, so as to not notice the noise that naturally comes in thru the walls.
Am wondering what you think of that idea? It is a small house, and will probably put these windows in all the bedrooms too, just to help quiet thing down through out the house. Will the 41 STC with one pane laminated keep the truck and flowmaster rumble down enough to warrant the trouble and cost? Thanks for any info you can give!
Mary V

An STC of 41 will be a noticeable improvement of what you have currently and will also address those mid level frequencies you are troubled by.

If it were more of a droning traffic noise, you would want to pay special attention to OITC for the lower range frequencies.