T25 Turbos are on the smaller side of turbo applications. They are great for 4 cylinder cars. Usually they are set for 7psi boost, but it's safe to use them at 13-15psi. The max boost is usually 17psi.
The T25 Turbo is one of the best options for daily driven FWD 4 cylinder cars...it gives you plenty of power without causing major traction issues, and you don't suffer any of the turbo lag that you'd get with the bigger turbos. The HP gain is usually 60% which translates into about ~70+whp gain. Which is great bang for the buck, since at this level you don't need to beef up your internals.