I've had 3 of them. (2 Rs and one regulargt350 that I turned into a track rat.)
They have to be driven hard, or the motor gets real unhappy.
The trans and rearend absolutely need coolers. If you buy a 16 with the comfort package, be prepared to add coolers.
They are the best performing track car for the least amount of money.
If I intended to still spend time on a racetrack, I'd get another.
lastly, you haven't lived until you bang through all 6 gears by taking that car to redline before each shift.
Best performing car for the least amount of money is still a used vette - C5 or C6, no engine failures, no oil starvation, no mods really needed (necessarily - although the skys the limit) to take a C5-C6 vette to a road course or HPDE drive the shit outta it & then drive it - not trailer it - back home. I do agree the GT350 is also one of the best bangs for the buck out there as well - especially on the used market (although they tend to hold value quite well) - I was never a Ford/Mustang guy, but there have always been a few I've been intrigued by - the 03-04 termi cobras & the 17+ GT350 w/ 5.2 voodoo @ the top of the list. Well when I went through a laundry list of cars taking on test drives while debating on messing around more w/ my current toy car (Z06) or "upgrading" to something different/more modern - the GT350 was one of the top cars I was interested in. After driving one 2x I was really enthralled w/ the handling - mind blowingly good especially considering my previous Mustang bias in that dept - I'd say on par w/ C5-C6 corvettes better than an M3 & close to the M2 I drove, & I obviously like the sound of the engine & the high redline...interior fit/finish little "meh" but layout nicer/more accommodating than a Camaro.
Since I am admittedly not a Ford guy, after test drives I put in a lot of research since it was one of the top cars I was interested in & one of the more expensive. Well.....shorten the story up for ya - I was too gun shy to pull the trigger after reading horror story after horror story in particular on GT350/GT500 specific forums where I was sure there was alot of knowledge & GT350 nerds, noisy/rattling shifter (which I thought was a first gen coyote 5.0 GT issue that was resolved already), outrageous oil consumption - like CRAZY CRAZY, & the real kicker - seized engines. Straight up dead. For a guy that can't help but mod his rides a little bit, the thought of catastrophic failure @ any time on a hand-built low volume flat pane V8 @ any point turned me away. The fact that 2 of the most common complaints I heard on the car popped up even on a C&D 40k mile review...well that sealed the deal for me personally. If you keep your cars mostly stock or don't intend on driving @ the track or really hard (which IMHO would be near impossible not to do all the time w/ the way this car sounds & pulls) - then go for it. I actually REALLY disagree on buying it if you WERE going to track it b/c of the fact the engine failures seem fairly common & Ford can be stingy w/ warranty claims.........another car I looked @ is the C6 Z06 which is also known to have a pretty much guaranteed (if you drive it long enogh) major engine issue w/ the valvetrain - gotta rework the valve guides/heads first & foremost for insurance - which if done aftermarket will probably void warranty too - in that particular car I didn't care as much as I know the rest of it is pretty much bulletproof & you can always swap out/upgrade heads port/polish get some other lil internal upgrades here/there & while at cam swap. But the valve guide/head job alone is around $2500-$3500 & then throw another $1000-$2000 for cam upgrade.
Bottom line - as tedious as it is, I've found it better to exhaust yourself on the forums ahead of time before making any "specialty" vehicle purchase especially.
https://www.caranddriver.com/reviews/a23083757/2017-ford-mustang-shelby-gt350-reliability-update-3/