I have used a pair of Trust T517Z on my GTR before with Cams, power FC, Exhaust, coolers etc...I was making 301kw@all wheels at 1.1bar
and now I up graded to pair of Tomei Turbos...still using the old T517Z maps in Power FC with heaps of lags making 394kw@all wheels....
if you are looking for cheap up grade..I can probably help you to get some brand new GTR replacement turbo (-10) for around $2900 to $3000. and with those turbos you can easily get over 340kw with stabdard internal.