As I understood it the KO4-001 was a hybrid version of the KO3.
This is what Tony (Jamiebennett81) has. The Hybrid version is supposed to be like the KO4-023 (a la LCR) so basically you'd be looking at getting apporox 270-
280 BHP with a quicker spool but still holding boost to the red line.
I doubt this would be a big enough jump for you Phil, I'd look more into doing your injectors and get a GT28R which would give you 320BHP easily.
My mate has the above turbo with INA exhaust manifold and he loves it.
For either the KO4-001 or a BT you won't have much more work to do just more cost.
So I'd say go for the GT28R, if you go for the KO4-001 you will want more power soon and kick yourself you didn't just go the whole hog the first time.
Also you'll need all that power to drag that lardy assed S3 seats around, lol