There is a step inbetween your stock T25 and the T28. It is the T25 on the grey and red top SR20's. It has a higher AR than the stock T25 but lower than the T28. It depends on how far you want to push your engine. It seems subjective and is different to whoever you talk to but 130-150kW is as far as you would want to push the stock comuter, injectors and internals. If you want more than that, you best get better management, injectors and some bigger legs. But tuning is more important on these little engines than most else. But you do hear of blokes getting around the 220kW mark with just some lower compression slugs, computer and the T25 off the SR with stock rods so it depends on who your tuner is.

hope this helps
mely