How much power should i be making once meth injected??

[The Godfather]

Im considering running water/meth injection and have been reading for a few weeks now on some of the benefits but am yet to read on power gains with different ratios.

a quick run down on my car and mods:
its a gsr/evo 3 mitsubishi

2.0L 4g63 fully forged internals, 8.3:1 comp ratio wiseco pistons, eagle rods, cometic 1.2mm head gasket, etc etc
GT35R turbo with .70 front 1.06 rear!
280 cams intake and exhaust
Hypertune intake manifold and throttle body
walbro internal and bosch 044 external with surge tank
750cc injectors
haltech E8 ecu
3inch exhaust

putting out around 270kw or 365hp at the wheels. @ around 7800rpm and roughly 20psi

just wanting to know how much power can be made on top with either 50/50 water/meth and other ratios. 40/60 20/80 etc obviously no one can give me an exact figure but a rough idea would be great. Car can be revved to 9000rpm reliably and can run about 24psi all day every day on pump fuel.

any help would be greatly appreciated.