I don’t have 94 where I live. But I spent way more than $2k. $2k for the turbo, $300 for the tune, another $100 for gaskets and bolts, then the down pipe, wastegate, intercooler, crossover pipe, intake, s hose for the intercooler, oil, filter, Cobb AP and $1k install (I have no tools or space or skill mechanically speaking). Probably around $5k all in. So yeah, it was tough to accept 280whp as a permanent stopping point. But it’s all my fault. I didn’t do my homework. I’m living the sunk cost fallacy big time now though 😅
Sunk cost fallacy infers the 280WHP was a mistake and now you are throwing more parts/money at it just to justify your original purchase. which isn't true in your case.
*everything* you installed were things you should install anyway to get to 280WHP on an S280. yes some of it doesn't help with power at all but it certainly helps with everyday reliability and everyone here would recommend everything you got regardless of ethanol or 93OCT tune. you didn't "get stuck" at that HP number. you reached the summit of what the Fiesta ST can reach with pump gas.
if you wanted to break past 280WHP and get north of 300 on your way to 350WHP, you'd need to upgrade the suspension (at the very least add some negative camber and maybe even positive front caster is a must); most likely the transmission too with an LSD and better clutch if you decided to go stickier tires to take advantage of the upgraded suspension to go with all that HP; and also upgrade your brakes (BBK is what most people do here but there are others who figured out ways to upgrade our existing braking). we're not even talking about upgrading your bushings, bracing, motor and tranny mounts (all of them), I COULD KEEP GOING.
yes you dropped $5K to get 280WHP to the ground. want to get 330WHP to the ground on the Fiesta? (first of all LOLOLOL, good luck) that would cost you $5K more. you're sending all that power to the front wheels. you're already at the point where the stock build is roasting those tires. think adding 330WHP only needs sticky tires? congrats, you just broke your tranny. think you don't need an LSD with that upgraded clutch? congrats, the "e-diff" is warping your brake rotors because now it's trying to rotate the car with 150 more horses to corral around corners. just the brakes you say and no LSD? fair. but now you're grumbling how the car doesn't have more speed coming outta corners than a stock Fiesta ST...lol, yeah the deeper down the rabbit hole you go the more you realize how much needs to get put into this car to get past 280WHP.
look up how much a performance car that gets 300+BHP (your engine clears 300 brake horsepower now easy) and see how much they cost; you saved *a lot* of money getting a Fiesta ST and getting to 300+BHP yourself.
pat yourself on the back for a job well done. don't beat yourself up over something that never could've been.
EDIT: all of this was written with the understanding maybe you would've never went down this road if you couldn't get 350WHP. maybe you would have bought a different car to get there or just done an easy whoosh hybrid upgrade and be done with it. i completely understand either feeling but still want you to know you did a good job here.