Before I got my BRZ in 2017, the Mustang GT was short-listed as well but I dismissed it back then even without a test drive. Back then, I thought to myself it's either the GT350 or forget about it.
The nagging etch was still there so I decided what the heck I'll just go give it a test-drive.
Please bare in mind, these are
MY thoughts on the Mustang GT. You might agree with me and you might not. Just sharing for the benefit of whoever wants to read.
Executive Summary

: very decent handling, numb steering, magnificent engine sound-track, surprisingly similar to FT86 in many ways, extra power did not impress, not as nimble as FT86,will not replace FT86.
So first, why would I be looking at the Mustang GT. My main shortcomings on the FT86 is power (or rather people always nagging about it all the time on reviews and whatnot) and engine sound.
First, the sound, the GT absolutely did not disappoint. Those are Diva vocals for cheap. It's a musical instrument that just wants you to play. The sound alone can justify the purchase no argument there. This is what I wish the FT86 even remotely sounded as good.
The interior dimensions were surprisingly similar to the FT86. Even the trunk space looked so familiar. The rear seats actually even lacked headroom next to the FT86! The seats are high though and you do not get that sports car feel as much as you do in the FT86 which is a big negative for me. The low slung feeling of the FT86 gives you confidence. The visibility outside is similar but the hood feels like it never ends. Like there's a piano in front of you.
The breaks were another surprise to me. I did not check to see if this Mustang GT had the Brembo package but I was noticing how they felt almost identical to the ones in the BRZ. I later checked and yup, both had the Brembos. I guess, I have new found respect for Brembo now.
The steering felt numb for me which is among the bigger negatives but more feelsome than a lot of front wheel drive performance vehicles (cough Focus ST). The handling was surprisingly really good. I obviously didn't get the chance to really push it hard but I was surprised for the lack body roll for something this heavy (and yes you can feel that you're driving a heavy car Vs. the FT86)
Now where I was really disappointed and I am surprised to have been disappointed, the Power! I am very sure this car is very very fast. All metrics prove this. But from the seat of the pants, this car is heavier and more insulated and going fast is one thing while feeling the speed is another as I've come to learn even more so this weekend when I participated in open wheel racing for the first time in my life. The sensation of speed was muted compared to the FT86 and this made a big difference for me personally. I would rather "feel" like I'm going fast when I am actually going slow rather than the other way around. I don't have an ego issue where I want to beat people in road-races or anything like that. And even in actual racing, I would still rather be driving an FT86. The throttle response is decent but nothing super impressive either. I'm sure the power difference is more felt at say 70 mph onwards but I won't be doing that much on public roads.
Overall, the Mustang GT gets a very big win in the sound department but actually looses in the power department for me personally just due to feel. Then there's the nimbleness of the FT86 and the steering that's more precise and talkative. Add to this, the fuel consumption that does matter to me for my lead foot tendencies and I'd hands down keep the FT86. I honestly do not want to come across as a fanboy. I don't have loyalties to a machine. All I care about is my personal utility of it. Make no mistake, if I liked the Mustang GT more I'd be right here saying it. But in all honesty, I personally did not.
Alright, you can fire away at me now

. Just be warned, I've noticed some forum members being unnecessarily on the hostile side here and I will ignore. If you have personal issues in your life, or feel the need to dominate others, whatever that's bugging you, I don't believe such forums are the place to resolve these issues of yours. I see such forums as a place for me to come and be stupid and learn a thing or two from others more knowledgeable without the need to be put down or me putting someone else down. Rant out.