I have fitted them with varying levels of modifications.
On a normal setup somewhere around 120kw would be about the limit.
On a really good setup if your pump is in pristine condition, you might get up around 150kw.
Also highly depends on the exhaust housing area ratio.
Dont expect to buy an mtq kit and have any decent amount of boost below 2200rpm (in essence making them useless)
You would be better off with a 16G vs the mtq kit by a long way.
a .48 rear housing will make it come alive before 2000rpm and it will be nay untouchable between about 1600-2200rpm. It will fall away heavily if you tune it up though due to the restriction that tight rear housing creates.
If you can tell us EXACTLY what you are hoping to achieve out of your setup myself and a few others can give you some decent pointers in which way would work best.