It will be loud. I have
these installed and it's pretty loud. I imagine the ones your looking at will only be louder due to the fact that they're basically a delete.
I agree tho... the Nismo is way too quiet stock. I love the sound now with just the axle-backs but I do feel like cold starts in the morning probably piss my neighbors off.
Plus, like Nixin said, putting these on comes along with a host of new vibrations to try and track down.
FI is definitely on my list of future purchases but for the price, the TopSpeeds were a great compromise for me.