Jon, I have been a long time Mustang owner and fan. I ordered a 2017 Mustang GT premium with the PP six speed manual. I don't have to tell you that the S550 is a complete redesign of the Mustang especially with the IRS. The engineers at Ford targeted making the S550 Mustang match or exceed the 2012 Boss 302 model. And that Boss is a very cool, wonderfully handling car. The S550 Mustang GT with PP is probably the BEST Mustang built (except for the Shelby & Roush variations). The handling and HP make it one awesome car.
I opted for the 5.0 and upgraded to the PP to make my car an even better handling car. So it all depends on what you want. The turbo is a great car with the right amount of HP. Personally I would never purchase another turbo car from Ford, been there done that. Besides I wanted the Coyote motor and the 435 HP. My car retailed for about $45,000. That is a lot of $$ for a Mustang.
Driving impressions? 435 HP is a lot of HP. Going from your 210 to 435 is going to be an amazing upgrade for you. I went from 320 HP to 435. The first six speed manual I test drove I spun the tires in the dealer parking lot. I've driven manuals all my life. (That had a lot to do with the HP & torque and that helper spring Ford puts on the clutch. I have replaced the clutch spring in mine with the Steeda 35lb. You can't feel the clutch engage with the stock spring.)
It has been a learning experience to handle 435 HP and with a manual. The sales guy suggested I get an automatic saying driving this car is challenging enough, do you really want to add a manual to make it more challenging. He was right, honestly. The PP add ons are worth the cost in my opinion. The PP brakes are beyond amazing. 60-0 in 105 feet is super car territory. Learning to brake this car is unique on to itself. It stops on a dime and gives you 25 cents change. Shortly after I got my Mustang I had it back to the dealer for some tweaks, I asked if there was someone I could discuss the car with. The Service Manager came out. First thing he said to me was "Are you the guy that purchased that red race car?" He is right, this is a race car.
It all depends on what you want. The base GT is a great car. Adding the premium and PP makes it an even greater car. I was talking to a friend last week that wanted to order a new 2020 Shelby GT 500. 700+ HP. I can't imagine why I would want that much HP. Seems like a guy thing for someone that wants to win the biggest
argument. 435 HP is plenty and a handful to manage. What is cool about my 17 Mustang though is if you drive it like a little old lady the car behaves very well. It has no problems with that. Step into it though and it awakens the beast. This summer I am going to teach my wife to drive my car. She can drive a 5 speed. But I need to teach her to respect what this car can do if you get into it.
So is it worth the money? To answer your first question, this is a huge bump up in HP from your V6. More than double. Imagine that. I was surprised at going from 320 to 435. Do you need that much HP? No. 300+ is plenty for a sports car. More can get you into trouble real easy. Is it worth the $$ to get 435? I would have ordered the V6 if I could have gotten the GT
suspension. For perspective, 435 HP in this car makes it faster than almost any prior comparable cars. All those classic Muscle cars have less HP and handle far worse. The S550 GT is in a rare class of cars.
One last thought. Knowing what I do now about these cars, I would have seriously considered ordering the V6 six speed manual, then upgrading the
suspension to the GT level with aftermarket parts. That would have been a very cool car. Just the right HP and handling. A big upgrade to your current Mustang. And if you want HP add a supercharger. Maybe you can find a used V6 since Ford stop offering the V6 in the Mustang.