Ive done a few sets of T618Z's and usually against my recomendations, the engine work required to make them work is extensive... but for your application they might fit the bill.
The T618z's are designed for drag and circuit use and i have personally been in a GTR with the 618's on a well setup TRUST car and it was awesome (700+ps @ 1.8bar), i supplied TRUST's receipe to a shop out sunbury way, including all the parts about 4-5 years ago but due to reasons i cant post it never performed.... shame as it was a waste and had heaps of potential.
Big cams, port work, big boost (they are rated 1.5 - 1.9bar) and rpm are needed to make them work, a nice white street / ciruit GTR here in melb (creatd built) has run low to mid 10's with a custom pair of garrets built by rotomaster to T618z specs... again with a built motor to suit... expect to turn your motor inside out.