I'm asking for a friend of mine. He's looking for a turbo that gives around 750 HP on 98 feul (Belgium) and 20% meth injection.. With all the choise you have in the turbo world he's getting crazy

small Speclist (there is lot more...):
- Iag 2.5 stage 4 tuff carters
- arrow billiet crankshaft
- Manley pro series I beam tuff rods
- JE time attack FSR pistons
- arp/iag 14 mm headbolts
- 2000cc injector dynamics
- brian crower cam shaft pulleys
- 2006 2.5 sti heads cnc constructed heads (supertech 1mm bigger nitrated inlet valves, supertech 1mm bigger inconel exhaust valves, super tech double springs, supertech retainers,
- kelford 282/278 camshaftset
- ...

 

quick online search and seen a 800whp impreza running the following

https://www.definedusa.com/Extreme-Turbo-Systems-Rotated-Turbo-Kit-p/ets-0407-sub-tk.htm

or contact RCM as they have a 780BHP impreza

https://rogerclarkmotorsport.co.uk/gobstopper-II

 

now thats a proper 2.5 build lol

owen developments does a very nice GT37 with extended tips ,, two of my mates have made 800bhp with it

 

WHP quoted in the US always seem to marry up with what's measured as bhp over here, and considering that their petrol is a few grades lower in a lot of states I've always taken such claims with more than a pinch of salt - unless they're actually winding the boost up so much they really don't care it seemed unlikely but who knows.
I'd check with SD Motorsport, Andy Forrest, Advanced Automotive or RCM, any of whom should be qualified to advise, plus any of the turbo manufacturers of course.