You my friend are in luck. You will most likely be ableto sell your 2008 2.5i and purchase a 05-06 LGT with much cash expenditure.
Its not just the turbo. Its the ecu, engine bay layout, brakes, etc, etc. There is a LOT more to a GT than just the turbo and HP.
That being said, several 2.5i owners seem to be very happy with their purchase even if its delta was somewhere near what it would have cost to just swap for a 2.5GT. Similar power to a bone stock 2.5GT just begging for mods.
Something to think about.