What should I take in account when using a more powerful triac?
Two things I would check:


the trigger current, your triac requires 50 mA. If this is more than the triac your circuit was deisgned for you might need some changes
cooling! At 25A your triac seems to dissipate in the order of 25 .. 35 W. At a Tc of 75C and an assumed Tamb of 40C this means a heatsink of 1C/W. That's not a small one!