I think the KA-t setup is solid if done correctly. I know guys that have done over 500 whp on a stock motor, relability is an issue at those levels. I have another friend that makes a reliable 300+ whp on his KA-t with plenty of road racing and autoX. Read thru his site KA24DEvelopment.com :: , check his links for the better 240 forums.
From what I have seen with other KA-ts the pistons are the weakest link. Make sure you have a good tune and you should be fine at a 200whp level. Why are you looking at the t25/t28 VS a t3/t4, are you looking for quick spool? All the KA-t guys I know are running t3/t4 series turbos.