Do you actually use coolant???

Radiator size is fine. It was fine previously wasn't it? Half size radiator has/is used 1000's of times by people with turbo setups, with no issues.

Brands, PWR, Koyo, Flyidine, Mishimoto. Have a look at the traders section on the forum.

Best way to make sure its the radiator is to take it out and inspect. Make sure it does actually flow.