Hello. Anybody have installed Garrett GT2854R in Coupe or I will be the first?

why would they?
they can squeeze same horses from the original turbo.

My idea is not just tuning and many horsepower (although this section is for tuning)! I care more how it feels the car with him!

Your idea isn't good . Drop-it ! Most of people there,use their coupe like everyday car...So,if they said 2854 si useless option..trust them;)
My 2860rs runs with absolutely NO problem,on stock internals engine for about 4 YEARS and about 60 dragraces...Full boost at about 3000rpm...almost like the (very poor) stock turbo ..isn't enought for you? If is not,stick to the tb28(std) turbo;). That 54mm compressor is good for offroad truck or for Fiat Uno turbo tuned for ..shopping:D..No offence mate !