I had the ATP GT2554R, the kit was lag city compared to stock. Took a lot of the fun out of the car. The bigger wheel within this 2554R will only help top end, spool will be essentially the same.
If you want 300whp or less, a hybrid is your best option. If you want 300+ then look into DHM kits.
I love more options hitting the market, but a slightly modified 2554R is not groundbreaking or a competitive option with what's already out there.
I was reading back through the thread and wanted to comment on your post now that I have this thing installed and on tune 3. I have 177.000 miles on my ride at this point. So a lot of experience on the stock turbo and while I am not a turbo expert I can comment on the ride. I also want as a reminder to put in perspective remember I have owned both a 800 and 1000 hp street Pontiacs and a 300/300 Fiero. So relative. As I have been driving around on this for a couple of weeks the instant take off or lack therof in which you speak is not as separate as you describe. My part throttle is insane compared to what the stock turbo felt like. Everyone here has a turbo in their car and has their own opinions and for me to say their is no lag would be a lie. But the difference is very very small compared to stock. Opinions are relative right? That's my opinion. If I was in 1st gear and put my foot down moving it ever so slowly I would notice the lag. What this turbo does is allow me to get moving and by doing so it reduces wheel spin. More on displacement below. Now, that is an overstatement as if you do not manage it with your foot even with traction control on you will blow the tires off in 3rd gear which I did this morning. I was asked not to reveal any numbers until the tune was complete but this mornings run was at 5:30 at 54 degrees. I'll let you just ponder that. The car is ballistic. I'm certain you all get that feeling with any turbo upgrade over 300, but the curve on this is so nice and smooth. Their is nothing erratic about it. I am so very pleased. I was a huge fan of the stock turbo on the ots Cobb stage 3 tune. Yeah I know right? Even with the minuscule amount of what you call lag, this is really in my opinion what this car should have been from the factory.
I stand by what I have said earlier. You can make anything go 500hp with enough money. This car making over 350 dare I say, 330 is more than you would ever need. If you need more you need more car. I mean it. Chassis design is something I understand and while you can do more in the car I think your pushing the physical envelope and reliability is out the window. Let's not argue about it their are plenty of people making 320+ that doesn't mean they should and it doesn't mean their not on the bleeding edge of reliability and safety. I know we have a focus st clutch and focus st axles but you have to take into consideration linear motion and the forces placed on the chassis under acceleration and deceleration cornering and braking and weight transference.
The other thing I noticed is that the spool down is slower than stock. Meaning as you approach red line to go from 1-2 2-3 3-4 4-5 under hard acceleration on the stock turbo it seemed like the rpm went down quicker where as this holds rpm longer.
You might want the hybrid if you were racing all the time on a road course because coming out of a turn the hybrid may give you an advantage, but based on my boost level and lbs of air moved versus with what I'm seeing, with the hybrid your not going to hold the lead in the straight away. You might pull off an 1/8 mile upset but not the 1/4. As a stout 1/4 mile guy I would be willing to bet this is the case of all the bigger non hybrid turbos. This turbo is making more boost than the reported hybrids so far based on the little access port and for much longer than the hybrids.
Now for displacement. This turbo is. Egging for a larger displacement motor. It could be a modified 1.6 to 1.8, it could be a 2.0 or a 2.3 ecoboost truxk motor. A little normally aspirated low end torque fro a larger displacement motor and this turbo it would be insane. The possibility exist to take the stock turbo and this turbo and do a compound setup(I'm still contemplating) but I think the bigger motor makes more sense. I guess we will see in April 2018.
Not trying to upset anyone here just giving my opinion based on my Mountune install. Let me say it again. I am so very happy with this turbo and would highly recommend it to anyone wanting to spend the least amount of money for the biggest bang for your buck from the most reputable company supporting our vehicle. It doesn't matter if it is a Garrett with Mountune's name on it. In my opinion if Mountune decided to put their name on it that made it worth it because they felt it met their standards. That they upgraded the turbine, if it was 5 blades or 20 blades who cares if the turbo is doing what they say it does, then it's worth it and it does more than what they say it does.
And as for the wastegate not changing it out. It is so not necessary. If I do anything else power wise this year it will be to install either or both a dei cro2 fmic sprayer, meth/water injection 8" before the throttle for safety.
I may have randy do a tune for race gas which I can get here easily for a drag day here and there.
This turbo is like buying a brand new car.