So I don't know much about wheel offset... From what I read on some other sites, it's important for responce and stuff but not needed to be exact.

I also read that the stock offset for 4th gen prelude is +55. That right?

What kind of diffrences would I see if I got rims that had a +42 offset? +45?

 

The lower the offset the further out the wheel will sit in the wheel wells. I'm not sure how far you can go with the 4th Gen but the 5th Gens are pretty safe between 44-50mm offsets on wheels from 6-7.5" width. Maybe some 4th Gen owners can help you better.