Thinking about trading in a 2013 Mustang GT for a Fiesta ST

Yes, really.

I'm just curious if i'm the only person out there thinking about making this jump.

A little backstory would be that I don't generally like big cars, or heavy cars but I do like good drivers cars. I've owned a very diverse mix of cars ranging from Japenese Econo-rally fighters to BMWs to my current Mustang. A year and a bit ago I bought a new 2013 Scion FR-S, but after about 8 months I grew tired of the lack of torque and no room inside. The step to a mustang was a strange one for me, I hadn't owned a muscle car (or even a Ford) before, but the Mustang was a competitor to much more expensive cars and really appealed to my inner redneck with its awesome v8 and good features but every time I think about the fiesta st I remember how the most fun i've had in cars has always been the cars that I could drive at 9/10ths on the road without worrying about being arrested or killing myself or someone else. It is much more fun to drive a 'slow' car fast than a fast car slow

Sso today I called my local dealer and told them I want to see the first Fiesta ST they get. I need to drive this car.

Also, don't get me wrong. I love my mustang and this isn't something i'm considering because I'm unhappy with it, but rather than I think I would actually have more fun wringing out a fiesta than carefully applying my right foot when the road is good enough. I will happily own it forever and I went into it knowing I was giving up some things - fuel economy, interior materials, etc... but my needs have moved on a little since buying it, so here I am trying to make this decision.

I have a couple of questions for anyone with relevant experience to answer

Interior quality - the mustang is not a car you buy for the interior. The steering wheel is not good, the dash is okay, the doors are gross and feel terrible. I've driven a top spec Focus and found the interior to be laughably better than the one in my Mustang. I'm wondering how the fiesta st compares to either? I'm not hoping for BMW levels of finish, but something other than hard plastic, and a steering wheel that feels like a hula-hoop.

Interior room - one of the problems I had with the FR-S was that I'm a tall husky guy at 6'6 and 280+ lbs. I fit surprisingly well in the mustang given that its coupe, but according to the spec sheets the fiesta st has even more headroom - they dont' always tell the whole story though.

Third question:

Am I insane?

Welcome to the community.

To answer some of your questions:
1) The Fiesta's interior isn't going to have the same level of fit and finish as the Focus, but for a vehicle in it's market, the interior is very nice. You won't find an abundant of cheap hard plastic as you do in the Honda Fit, Toyota Yaris or even a Civic. Even the dash is made from a solid plastic that you would find in more expensive models. Additionally the interior road noise is very low for a car it's size, which is great for long distance driving. You should drive the FoST and the FiST back to back like I did. You'll probably agree that the Fiesta handles much better.

2) I'm not as big as you are, but my salesman was 6'4 and he didn't have any issues with head room or getting in and out of the Recaros. If you get the moonroof, you'll still have another inch or so of headroom.

3) Welcome to the insanity.

Thanks for the welcome
So the moonroof gains headroom? Interesting. Past cars I've owned usually lose an inch or two for a sunroof or moonroof option due to the need for the 'cassette' the sliding section is stored in when it is open.

I have a friend who is waiting for his Focus ST to be delieverd, I'm going to wait until he gets that to make my decision, as I'm still considering the Focus as well but I have a big soft spot for tiny turbo cars.

Sorry let me rephrase, you don't gain the headroom with a moonroof, but you don't loose alot because it's wide enough where your head can fit underneath the indentation.

Agreed 100% with MK, my wife has an 11 ses fiesta and its interior is more than i expected it to have. and like you said Reason, "It is much more fun to drive a 'slow' car fast than a fast car slow"
only this car isnt that slow. yes it will be slower than your 5.0 but quick enough for a sub compact. and this is the most powerful version of this engine that has been produced, and weaker versions have been in the fusion and explorer and yet they put this most powerful version in their lightest car. cant wait for mine. good luck and welcome to the insanity.