Yes you can boost a stock 2.5L and see 300 wHP with good conservative tuning and a properly sized turbo. The 3L just gives you better low end torque and more overall power.
Former owner of '99 CSVT - Silver #222/2760
356/334 wHP/TQ at 10psi on pump gas!
See My Mods
'05 Volvo S40 Turbo 5 AWD with 6spd, Passion Red
'06 Mazda5 Touring, 5spd,MTX, Black