I was wondering since i already finished the witcher 2 a while back when it came on the roches path, i was wondering how massive is the story difference is i say take ioverths path

Quite a lot in acts 2 and 3. I'm replaying at the moment, and I'm pleasantly surprised.

When I played the game for the second time, choosing Roche over Iorveth at the end of Chapter 1, it felt like a whole new game. The story is very different, and I always advice anyone who has just finished their first playthrough, to start a second one, trying out the other path in the story; you won't be disappointed at how well they complement one another and how the two of them combined give you a better understanding the entire game world and its story.

The replay will be massively different.. :)