Ive never seen a 2.5 but people on here have said they are very similar to schwalbe 2.35
I have however used all the schwalbe 2.35 and currently got a forekaster 2.6 and ardent race 2.6 setup on a boardman fs pro, although they are only a tiny bit wider they have much more height i.e. probably the overall diameter has gone around 1/2 inch, they feel like they have a much greater volume and seem to run well at much lower pressures.
Small bump compliance has definately improved and it rolls much faster on rocky terrain for the same amount of effort. Feels a tiny bit slower on the road but the trade off seems worth it
Btw i absolutely smashed mine down the rockiest of descents without a good line and pressures were 16psi front and 19 rear (i weigh 65kg), no punctures!