As Matt said, it all depends on where you ride, what you ride and how you ride. If for instance you're on a HT, then going to the 2.6" will make a nice improvement in comfort moreso than if you were on an FS. Also if as said you ride someplace with flatter or less fast terrain with maybe softer surfaces like sand, then it will help there, descending fast stuff, depending on the surface it might be better or worse. Climbing is another area you should experience some improvements in rolling speed, yet also traction, as the bigger footprint will get you just as much if not more traction than the narrower, slightly more aggressive tread.
So the reality of it is that you already bought and installed the tyres, give them a go and find out for yourself just how they change things. The one thing I would ask/say, is if you are on rims that are narrower than i30, you will not get the full benefit of the wider tyres and may not experience all the positives as much as if you were.
