I don't know why you didn't just buy the correct ones directly.
Plate at 250+ hp/liter not very good idea imo.

G25-660 full boost will be 4500+ rpm.
No way to reach full boost until 3rd gear without launch control.

1st and 2nd gear car will be much slower than something with 400hp unless using launch with antilag.
Third gear will be about equal to a 400hp car, and it will be faster in 4th gear and up.

Undrivable in the city, only good for drag race and autobahn.

Anything with a GT30 turbine will spool after 4000 rpm.
If you fit too small AR you will just have massive surge.

try custom turbo like gtx3067r gen2
only possible make aftermarket and small turbine housing
67 compressor wheel max 450-480hp
better spool like 3071or 3076  and top end i think good enough
and gtx30 wheel better low rpm than G25-G30
g25-550 good low rpm but very small compressor wheel and max hp approx 440

As I said before, anything with a GT30 turbine will spool at 4000+ rpm.
Including all the GTX turbos, they still use a GT30 turbine. If you want to use an older turbo (GT style) then you will need to go to the GT28 turbine to have sub 4000 rpm spool.
I see no reason to use one of those. G25-550 or the small EFR are reasonable choices, they will give you a roughly 3500-3600rpm full boost.

There is no magic fairydust here, as was said before many times.
You can make a 420hp decently drivable car or you can make a 500hp lagmonster.
Choice is yours, but in city driving the 420 hp variant will be always much faster, in every situation except for starting from full launch control at light.

This realization comes pretty hard to people, that bigger turbo on tiny engine is not always better, it really depends what the car is used for.
If you want to sit at every traffic light in launch control like a retard then go ahead and fit a GTX3071, but why not use a better more modern turbo such as the EFR7163 in that case? On the 1.8T you will have full boost at 4300-4400 rpm on this turbo. And this is in higher gears. In the 1st gear you will not reach the full boost without launch control, in the 2nd gear maybe at the very end, but probably also not. Same goes for the GTX3071 Gen2.
The car will make full boost starting with 3rd gear... 3rd gear 4300 rpm is over 100km/h so the car is useless in city.

With the smaller 400-420hp turbos you will have full boost already in 2nd gear at 5000rpm or so, even without launch control.

I remember over 10 years ago doing a test with a friend on an old airfield.
He had a 700hp 2.2T Audi S4 and I had my 480hp RS4.
We started both in 3rd gear at low rpm. By the time he got on boost, I was in 5th gear and half the airfield away from him
With rolling launch or starting at high rpm no chance for the RS4 of course. But this is not what happens in city driving.

So it is kinda funny how you say 4000 rpm is laggy but you're trying to choose turbos that will give you max boost at 4500 rpm in high gears. Make up your mind what you want, then get turbo for power target.
I think for 400-420 hp you can also get away with the 8.5 pistons, so you don't have to bodge anything.
But if you want to make a dragstrip car or for autobahn then you can easily go to 7163 or G25-660 and 8.0 or even 7.5 or so CR (tbh I'd do 8.0 + WMI), and have lots of fun at high speed. Driving in city it will be like N/A.

In the end with the modern cars you have to think that a 3.0 BTD or 35d bmw also makes 400hp with just a remap, and everything is full of those, and they have nearly no lag (and are boring as hell). Your car is lighter, so it will be faster, but if it has a huge ass turbo on it, then the diesel will be at the next lights by the time you spool lol.